# A brief explanation of the theoretical framework

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This chapter will provide a brief explanation of the theoretical framework of the study. Then it will examine the theoretical and empirical literature on Van Hiele theory of geometric thinking. Consequently review and discuss on literature involving van Hiele theory and dynamic geometry software, follow by review of literature on teaching and learning of geometry by dynamic geometry software Cabri 3D as an instructional tool. Then chapter conclude by review literature on designing learning activities.

## The Van Hiele Theory of Geometric Thinking

The van Hiele model of geometric thinking is one theory that offers a model for explaining and describing geometric thinking. This theory resulted from the Dutch mathematics educator doctoral work of Dina van Hiele-Geldof and Pierre van Hiele at the University of Utrecht in the Netherlands which completed in 1957. Pierre van Hiele formulated the five levels of thinking in geometry and discussed the role of insight in the learning of geometry in this doctoral thesis. Van Hiele reformulated the original five levels into three during the 1980's. Dina van Hiele-Geldorf's doctoral thesis, which was completed in 1957, focused on the role of instruction in the raising of a pupil's thought levels. Her study centered on thinking of geometry and the role of instruction in assessing pupils to move though the levels.

The following summary of Van Hiele theory is taken from Hanscomb,Kerry, 2005, (p.77): A convenient location for many primary sources on the Van Hiele model is Fuys et al. (1984).Other primary sources are van Hiele and Van Hiele-Geldof (1958) and Van Hiele (1986). Secondary sources for Van Hiele research are Mayberry (1983), who found that students may operate at different levels for different concepts; Mayson (1997),who claims that gifted students may skip van Hiele levels; and Clements and Battista (1992),who cite finding indicating that the van Hiele levels involve cognitive developmental factors as well as didactical factors.

The van Hiele theory has been applied to clarify students' difficulties with the higher order cognitive processes, which is necessary to success in high school geometry. In this theory if students do not taught at the proper Hiele level that they are at or ready for it, will face difficulties and they cannot understand geometry. The therapy that offered for students by this theory is that they should go through the sequence of levels in a specific way. (Usiskin, 1982b). It is possible to generalize the Van Hiele model to the other topics such as physics, science and arts. Because the main idea of this theory is the consequence of levels and believing that each level is built on properties of the previous level as many researches has done based on this theory on science education.

## Characteristics of Van Hiele level of geometric thought

Van Hiele theory argues there are some misconstructions in teaching of school mathematics and geometry, which was existed for long time based on the formal axiomatic geometry and was created by Euclid more than two thousand years ago. Euclid logical construction is based on his axioms, definitions, theorems, and proofs. Therefore, the school geometry that is in a similar axiomatic fashion assumes that students think in a formal deductive level. However, it is not usually the case and the students have the lack of prerequisite understanding about geometry. Van Hiele discusses this lack creates a gap between their level of geometric thinking that they are, and the level of geometric thinking that they required for and they expected to learn. He supports Piaget's points of view "Giving no education is better than giving it at the wrong time". Teachers should provide teaching that is appropriate to the level of children's thinking. Van Hiele theory suggests: It depends on the students' level of geometric thinking the teacher can decide in which level the teaching should be begun.(Van Hiele, 1999)

According to the van Hiele theory, a student moves sequentially from the initial level (Visualization) to the highest level (Rigor). Students cannot achieve one level of thinking successfully without having passed through the previous levels. Furthermore, Burger &Shaughnessy (1986) and Mayberry (1983) have found that the level of thinking at an entry level is not the same in all areas of geometry.

During last decades many researchers and investigators tried to support the Van Hiele model or disapprove of it and still some try to improve or adjust this model. Many of the researcher used Van Hiele level of geometric thought as a suitable and proper theory in their research using dynamic geometry software (Smart, 2008).

The Van Hiele levels have certain properties specially for understanding the geometry. First of all, the stages have fixed sequence property. The five levels are hieratically, it means students must go through the levels in order. He/she cannot fit in level N without having gone through the previous level (N-1). Students cannot engage in geometry thinking at higher level without passing the lower levels.

Second property is adjacency of the levels. At each level of thought what is essential in the previous level become extrinsic in the existing level. Individual understanding and reflection on geometric ideas are needed to move from one level to the next one, rather than biological maturation.

Third each level has its own symbols and linguistic and relationships for connecting those symbols. This property is a distinction of the stages. For example when a teacher use a language for higher level of thinking than students level of thinking, students cannot understand the concepts and try to just memorizing the proofs and do the rote learning. In this case miscommunication emerge (Hong Lay, 2005).

The next characteristic, clarifies two persons in different levels cannot understand each other. As each level of thinking has its own language and symbols so students in different levels cannot understand each other.

Lastly, the Van Hiele theory emphasize on pedagogy and the importance of teacher instruction to assist students' transition through one level to the next one. This characteristic indicates that appropriate activities which allow students to explore and discover geometric concepts in appropriate levels of their thinking are the best activities to advance students 'level of thinking.

## Phases of learning geometry

Van Hiele theory defines five levels of learning geometry which students must pass in order to obtain an understanding of geometric concept. To progress from one level to next level should be involve these five levels as Usiskin argued:

"The learning process leading to complete understanding at the next higher level has five phases, approximately but not strictly sequential, entitled:

Inquiry

Directed orientation

Explanation

Free orientation

Integration" (p.6)(Usiskin, 1982a).

These five level are very valuable in designing activities and design instructional phases.

## Phase one: Inquiry

First phase of learning geometry starts with inquiry or information satge. In this stage students learn about the nature of the geometric objects.in order to design appropriate activities, Teacher identify students' prior knowledge about new concept which need to be learnt. Then teacher design proper activities to encourage and encounter students with the new concept which is being taught.

## Phase two: Directed orientation

During this phase while students doing their short activities with set of outcomes like: measuring, folding and unfolding, or geometry games, teacher provides appropriate activities base on students' levels level of thinking to encourage them be more familiar with the concept being taught.

## Phase three: Explanation

As the name of this phase demonstrates, in this stage students try to describe their learning of new concept in their own words. Students in this phase start to express their conclusions and finding with their other classmates and teacher in their own words. They communicate mathematically. The role of teacher in this stage is supplying relevant mathematical terminology and language in a proper manner, by using geometrical and mathematical language accurately and correctly.

## Phase four: Free orientation

In this phase geometrical tasks that appeal to numerous ways is presented to the students. This is the students who decide how to go about accomplishing these tasks. As the way of solid geometry, they have learned to investigate more complex open-ended activities.

## Phase Five: Integration

In this stage students summarize completed tasks and overview whatever they have learned to develop a new network of concepts. By completing this stage it is expected that students attained a new level of geometric thought.

One of important properties of these phases of learning in Van Hiele theory is not linear in nature. Sometimes students need a cycle form of these phases by repeating more than one time to overcome certain geometrical concepts. The role of teaches here is providing suitable activities based on these five phases to develop each level of van Hiele geometric thinking.

## The Van Hiele level of geometric thinking

According to Van Hiele theory, the development of student's geometric thinking considered regarding the increasingly sophisticated level of thinking. These levels are hierarchies and able to predict future students' enactment in geometry(Usiskin, 1982a). This model consists of five levels in understanding, which numbered from 0 to 4. However, in this research we defined these levels from 1 to 5 to be able categorize students, who are not fitted in the model as level 0.

Level 1, Visualization

Level 2, Analysis

Level 3, Informal deduction

Level 4, deduction

Level 5, rigor

## Level 1: Visualization

The base stage of Van Hiele geometric thinking which is encountered with goals of mathematical domain is Level 1. The objectives of the first level are functions like the underpinning elements of everything that are going to be studied.

Understanding at this stage includes visualizing base objects. At this level visualization defines as comprehension or seeing initial objects in students' minds. For instance, a number line in this stage could be defined as real numbers in the domain of real numbers. Vectors and matrices can be seen as basic objects in the domain of leaner algebra. So perceiving vector as a directed segment or matrices as a rectangular table of numbers lies in level 1.

Elementary teachers know that it takes a few years of school for pupils to master visualization level. For example, it takes long time for students to see real numbers in a number line format. Similarly, perception of an ordered list or array of numbers, or an ordered pair of points is not something that occurs to an untaught mind and eye. Hence, serious teaching effort and introduction needed to students achieve Level 1and it is not assumed the visualization of initial objects to be obvious or trivial for students.

Geometry in Iran starts in elementary school and continues until level 8 with introducing geometry shapes like circles, squares, triangles, straight lines, etc. At the level 1 student learn to recognize geometric characteristics in objects that can be physically seen. At this stage student are assumed to be able to categorize geometric shapes by visual recognition, and know their names, for example, in solid geometry in level 1, if shown a picture of a polyhedron like a cube, students would be able to say that it is a cube because it looks like one for him or her. At this stage, it is not required to think of a cube, or any other geometric object, in terms of its properties, like saying a cube has 6 faces and 12 edges.

With visual recognition a student would be able to make a copy, by drawing, plotting or using some sort of dynamic geometry software, of a shape or configuration of shapes if they could be shown or told what it is they were supposed to be copying. In this stage, the instruction should be based on the name the student has memorized for the object and not the object's properties. For instance, it could be "draw a cube" not draw a "polygon with 12 equal edges that are perpendicular to the base and 6 equal faces.

## Level 2: Analysis Stage

At analysis stage, students begin to analysis objects that were only visually perceived at pervious level, identifying their parts and relations among these parts. They focus on the properties of these objects. For example, focus on Real Numbers in this stage can be closure under operations. This property can be leading to distinguishing subsets of Real Numbers inside the set which are Integers and Rational Numbers.

In solid geometry, the analysis stage is where students begin seeing the properties associated with the different shapes or configurations. A cube will now become a shape with 6 equal faces which opposite faces are parallel and 12 edges and adjacent angles right angles and having opposite faces equal, as well as having the diagonals intersect in their middle. However, at this stage, it is not assumed that students will be seeking logical relationships between properties such as knowing that it is enough for a Parallelepiped as a solid with parallel opposite faces and all the other properties follow. Neither is it assumed that students will think about a cuboid as a special type of Parallelepiped. Therefore, students will identify shapes and solids based on the wholeness of their properties. In other words, relationships between shapes and configurations remain merely on the list of properties they have.

At this stage if a student were asked to describe a shape or solid, the description would be based on the object's properties. At the same time, if a student were asked to reproduce a shape or solid based on the list of properties, they would be capable of do so. Students would also be able to verify figures and solids hieratically by analyzing their properties. In this stage student can recognize the interrelation between figures and their properties. For example, knowing the property that the Parallelepiped the student would be able to deduce that cuboid is special kind of Parallelepiped.

## Level 3: Informal Deduction Stage

Informal deduction is known as the third level of geometric thinking. Some of researchers name this level as abstract/Relation level too(Battista, 1999; Cabral, 2004). In this stage students can reason logically. This stage is achieved when a student can operate with the relation of figures and solids and is able to apply congruence of geometric figures to prove certain properties of a total geometric configuration of which congruent figures are a part. They become aware about sufficient and necessary condition for a concept. A student fit at this level after achieving pervious levels (visualization and analysis).

At this level emphasis is relations among properties. In other words, in this stage focus is "properties of sets of properties". Students in this stage attempt to group properties into subsets based on relationships between them. They will aim to recognize properties that are equivalent in certain situations and also be able to recognize the minimum amount of properties needed to describe one of the initial base elements. Overall, the main focus here is on the many different mathematical relationships between the properties. Finding and understanding these relationships is a type of informal deduction.

For the Real Numbers, it would be at this level that students would start to develop the idea that some properties of operations and order in real numbers follow from a small set of basic properties, thus making a step towards understanding the axioms of the Real Numbers as an ordered commutative field. But it only at the next stage that they would be able to produce proofs of such informal observations. That's where using the tools and techniques of algebra would start to play an important role.

Understanding Geometry at the informal deduction stage is a big leap for most students. Students would now be able to place properties into sets and identify the minimum amount of properties needed. A square, which might have had at Level 1 the properties of four equal sides, four equal angles, equal diagonals and parallel sides would now be described with a smaller set of properties like four equal sides and four equal angles. From this, students would now start formulating definitions for classes of figures. For example, a triangle would be defined as an enclosed shape with three rectilinear sides and a right triangle would be defined as a triangle where one of the angles is a right angle (or two sides are perpendicular). Students would also be able to recognize subsets of geometric objects or figures. Rectangles and parallelograms would no longer be independent shapes. Instead, rectangles would now be a special type of parallelogram. Students would also start to recognize which properties were subsets of each other. For example, having four parallel sides and four equal angles infers that the diagonals are also equal.

One of the most important aspects of this level of Geometric thinking is that students start to think deductively about Geometry. At this level a student would be able to give informal arguments to prove geometric results. These arguments might follow the simple logic of something similar to stating that if angle A = angle B and angle B = angle C then angle A = angle C. Or given a triangle ABC, if the midpoint of AB was T and the midpoint of AC was S and if TS was parallel to BC then BC = 2TS.

Students would also be able to justify arguments they are presented with informal logical relationships. Thus, at this level a student can use and give informal deductive arguments about previously known properties. As well, a student could use deductive arguments to discover new properties. Overall, students now start to recognize the importance of logic and deduction in Geometry.

## Level 3: Deduction

The third level of van Hiele theory is deductive level. Students in this level can construct rather than memorize proofs. They can undrestad differences between same proofs.

The objective of Level 3 is the organization of the statements about relationships from Level 2 into deductive proofs. At Level 2, relationships among properties of the base elements were discovered. At Level 3 these relationships are used to deduce theorems about the base elements according to the laws of deductive logic.

Referring to the Real Numbers example, it would be at this level that students would be expected to prove, for example, that for all real numbers a and b, (-a)(-b) =ab.

At this stage students are ready to accept a system of definitions, axioms (or postulates) and theorems. What was previously informally proved at Level 2 using diagrams and informal arguments can now be formally proved using definitions and axioms. Students can now create the proofs from the axioms and only use diagrams or models as a support for the argument. Students also begin to recognize the need for undefined terms in Geometry, which can be a very hard concept to understand in a purely logical system. At this level students also start to identify and understand the difference between a theorem and its converse, and contrapositive. They would also be able to prove/disprove any of these relationships. Students would also be able to see connections and relationships between theorems and group these accordingly. Thus, we have now reached the level at which traditionally high school Geometry has been taught in North America.

## Level 4: Rigor

Level 4 looks at relationships among the organizations identified at Level 3. In other words, the deductive proofs from Level 3 are now hyper-analyzed. This analysis looks for associations between the proofs. For example, at this level the questions of "are the proofs consistent with each other", "how strong of a relationship is described in the proof and "how do they compare with other proofs" would be asked. The level of Rigor involves a deep questioning of all of the assumptions that have come before.

This type of questioning also involves a comparison to other mathematical systems ofsimilar qualities. For example, in Level 4 if we considered Real Numbers we wouldbegin to compare them as a field to other fields in general. It is fair to say that this levelis usually only undertaken by professional mathematicians.

Level 4 of geometric understanding is very rarely met by high school studentsand is sually only attributed to further postsecondary education at college oruniversity, if even then. Here, students have the ability to work in geometric systems that are non-Euclidean and thus, the system usually is not able to produce a lot of visual models for recognition or rather that the models produced are not very useful and thus, focuses mainly on the abstract. Most of the Geometry done at this level is strictly theoretical, done on an abstract, proof-oriented basis. At this level students are able to compare axiomatic systems, like Euclidean and non-Euclidean. Students who have also reached this level are able to carefully develop theorems in different axiomatic geometric systems. Therefore, as was mentioned initially, this is usually the work of professional mathematicians and their students who conduct research in different areas of geometry.

The Van Hiele started his research after he found that most of the students have difficulty with learning geometry. He observed that these students struggled with geometry, although they easily understood other mathematics topics. The results of their study showed, most of the High school students are taught at level 3and 4. Then van Hiele deduced most of the students had difficulty in learning geometry at level 3 and 4, because they could not understand geometry at level 2 to be able to move onto grasping level. Therefore, for melting this problem more focus is needed at second stage, analysis level and more emphasis on third stage, informal deduction. Then it can be expected that they are able to success at the deduction level.(Battista, 1999)

Van hiele noted that students should pass through lower levels of geometric thinking smoothly and master them before attaining higher levels. Van Hiele theory recommends achieving higher level of thought needs a precise designed instructions. Since students are not able to bypass levels and achieve understanding, permanently dealing with formal proof can cause students to relay on memorization without understanding. In addition, geometric thinking is inherent in the types of skills we want to nurture in students.

## Research involving the van Hiele Model of Geometric Thinking and Interaction with dynamic geometry software

Van Hiele described in his article (1999) that the learning geometry can be started in a playful environment to explore geometrical concepts with certain shapes, and properties, parallelism, and symmetry. He advised some mosaic puzzles in this purpose. In the line of his work, geometry based software provide the more powerful environment which can be used to enhance the level of geometric thinking. There are several studies carried out on effects of using some dynamic geometry software such as (geometers' Sketchpad) GSP on levels of van Hiele .

Different researches had been involving the Van Hiele geometric thinking since last decades. Some researchers used van Hiele Model as the theoretical framework while others used it as an analytic tool. Moreover many researches conduct study on geometric softwares like: Geometry Scratchpad used van Hiele theory to find out their effects on geometric reason, geometric thinking and other aspects.

In order to find out whether dynamic geometry software is able to enhance the level of geometric thinking or not several researches has been conducted. In general, the van Hiele Model has been used in their research as an analytic tool and theoretical framework. For example, July (2001) documented and described 10th-grade students' geometric thinking and spatial abilities as they used Geometer's Sketchpad (GSP) to explore, construct, and analyze three-dimensional geometric objects. Then he found out the role that can dynamic geometry software, such as GSP, play in the development of students' geometric thinking as defined by the van Hiele theory. He found there was evidence that students' geometric thinking was improved by the end of the study. The teaching episodes using GSP encouraged level 2 thinking of the van Hiele theory of geometric thinking by helping students to look beyond the visual image and attend to the properties of the image. Via GSP students could resize, tilt, and manipulate solids and when students investigated cross sections of Platonic Solids, they learned that they could not rely on their perception alone. In addition teaching episodes using GSP encouraged level 3 of the van Hiele thinking by aiding students learn about relationships within and between structure of Platonic solids(July, 2001).

Noraini Idris (2007) also found out the positive effects of using GSP on level of Van Hiele among Form Two students in secondary school. In addition she reported the positive reaction of students toward using this software in learning geometry.

In contrast Moyer,T(2003) in his PhD thesis used a non-equivalent control group design to investigate the effects of GSP on van Hiele levels. His research carried out in 2 control groups and 2 experimental groups in one high school in Pennsylvania. He had used Van Hiele' tests written by Usiskin. However, Comparison of pre-test and post-test did not show a significant difference on increasing Van Hiele level of geometric thinking(July, 2001; Moyer, 2003).

Fyhn (2008) categorized students' responses according to the van Hile levels in a narrative form of a climbing trip(Fyhn, 2008). The theoretical framework used Smart(2008) for his research" Introducing Angles in Grade Four" was a combination of a teaching theory called Realistic Mathematics Education (RME) and a learning theory called the van Hiele Model of Geometric Thinking. His research findings suggest the usefulness of using lesson plans based on the two theoretical frameworks in helping students develop an analytical conceptualization of mathematics. In this study the model was neither proved nor disproved but just accepted as an analytic framework.

Gills,J (2005) investigated students' ability to form geometric conjectures in both statistic and dynamic geometry environments in his doctoral thesis. All participates were exposed to both environment and take parted, up to eight lab activities. He also used van Hiele theory as the main theoretical framework with more emphasis on geometric reasoning.(Gillis, 2005)

Research that used the van Hiele Model as an accepted framework covers variety of different topics. For example, Gills,J (2005) find out the mathematical conjectures formed by high school geometry students when given identical geometric figures in two different, dynamic and statistic of geometric environments. Burger and Shaughnessy (1986) tested students from grade one to first year of university to determine in what level the students are functioning regarding triangles and quadrilaterals.

## Cabri 3D

Most of the dynamic geometric software until 2005 has been constructed in 2 dimensions. Just a few dynamic geometry software, has constructed on Three-dimensional dynamic geometric software such as, Autograph and Cabri 3. Focus of present study is on Cabri 3D, which is a new version of Cabri II (2 dimensional software). Cabri 3D is a commercial interactive geometry software manufactured by the French company Cabrilog for teaching and learning geometry and trigonometry. It was designed with the ease-of-use in mind.

Cabri 3D as dynamic and interactive geometry provides a significant improvement over those drawn on a whiteboard by allowing the user to animate geometric figures, relationships between points on a geometric object may easily be demonstrated, which can be useful in the learning process. There are also graphing and display functions, which allow exploration of the connections between geometry and algebra. The program can be run under Windows or the Mac OS(CABRILOG SAS, 2009).

From Euclidean geometry, Compass, straightedge and ruler, for many years, have been used in as the unique method of teaching and learning geometry, and tools used to aid people in expressing their knowledge. With the creation of computers, new world opened up to teaching and learning geometry. The speed and memory of modern PCs, together with decreasing prices, have made possible the development of `virtual reality' computer games making use of the 3D graphics chips included on modern' graphics cards. some educational spin-off from this has been the development of 3D interactive geometry software such as Cabri 3D, Autograph ,etcâ€¦

But tools can contain particular conceptions so; the aim of designing a dynamic geometry software package is to provide new instructional tools to study, teaching and learning geometry. While all the dynamic geometry software attempt to model use of straightedge, compass and ruler in Euclidean geometry, other futures like measuring capability and dragging possibilities and changing the view of objects in 3 Dimensional (Gonzaílez & Herbst, 2009).

Cabri 3D launched in September 2004 by Cabrilog, this software has the capacity to revolutionize teaching and learning of 3D geometry, at all levels, in the same way that dynamic geometry software has for 2D (CABRILOG SAS, 2009). Cabri 3D can share the same aptitude for making new discoveries as a research tool. There are some important practical features of Cabri 3D. First, This program is capable to store the files as text in Cabrilog's development of the 'Extensible Markup Language' (XML). XML is the simplest version of the SGML standard for creating and designing HTML documents (suitable for use on Internet sites).XML designed by the World Wide Web Consortium as a more flexible replacement for HTML. Next, as Oldknow discussed, Files developed in Cabri 3D can be inserted as active objects in web-pages, spread sheets, word documents and etc. It is an interesting future because this objects which inserted in the files can be manipulated by users who do not own a copy of Cabri 3D in their computers.(Oldknow, 2006)

One of the important charactirisitc of Cabri package is draging.Arzarello, Olivero, Paola, &Robutti (2002) found that dragging in Cabri allows students to validate their conjectures. They claimed that work in Cabri is enough for the students to be convinced of the validity of their conjectures. If the teacher does not motivate students to find out why a conjecture is true, then the justifications given by students may remain at a perceptive-empirical level. Students would claim that the proposition is true because the property observed on the Cabri figure stays the same when dragging the drawing, given the hypotheses do not change. When such a belief is shared in the classroom, then Cabri might become an obstacle in the transition from empirical to theoretical thinking, as it allows validating a proposition without the need to use a theory. These researcher asserted, if teacher makes explicit the role of proof in justification, then students will be motivated to prove why a certain proposition is true (within a theory), after they know within the Cabri environment, that it is true. To paraphrase Polya (1954), first we need to be convinced that a proposition is true, then we can prove it.(Arzarello, Olivero, Paola, & Robutti, 2002).

In some researches the centrality has given to dragging in 2D dynamic geometry software and its implications for developing different types of reasoning (Arzarello et al. 2002).in addition because dragging is something which might make motion in 3D (on the 2D screen), it is more difficult to interpret and understand by the user. The various aspects of dragging in 3D DGE are issues that could usefully be the focus for research.(Hoyles & Baptiste Lagrange, 2010)

Jones, Keith and Mackrell, Kate and Stevenson, Ian in chapter four of Mathematics Education and Technology-Rethinking the Terrain book (2010) discussed that there are some set decisions that the designer of dynamic geometry software should make. One of these set of decisions is about how the 3D objects would look on-screen. For an object and its surfaces some characteristics should be noticed to have a 3D perspective and appearance. The designer should decide the ways in which the visual appearance of a 3D on-screen object depends not only upon its geometry but also upon the viewpoint by making use of lighting, shading, and, where appropriate, texture. These characteristics in programing and designing software call rendering. In terms of perspective, the default for the Cabri 3D is one-point perspective. The default viewing distance is 50 cm, representing the screen at arm's length from the viewer's eye, chosen as it was thought to be natural (Hoyles & Baptiste Lagrange, 2010). See Figure------

Figure 1:

A Snapshot of Cabri 3D

Figure 2:

Snapshot of Autograph 3

If we compare Cabri 3D with the Autograph, obviously the viewing distance chosen for Autograph 3 is more subjectively and shorter than Cabri. In addition, both Cabri 3D and Autograph 3 use shading, In terms of rendering. It means in both of these DGS, brightness of a surface is dependent on the direction in which it is facing relative to the inferred observer. But fogging is a unique ability for Cabri 3D which is not exist in Autograph. Fogging is a computer graphics terms for the effect by which objects at a distance appear to be fainter than objects close at hand. These characteristics is shown in figures ----

Using the mouse is further set of decisions relate to dragging objects, which should be considering by the software designers. On a flat screen Dragging only can give motion in 2 dimensions. For Cabri 3D dynamic software a decision was made that normal pressing and dragging can move the point and object parallel with the base plane. While dragging and pressing Shift key in the same time can move the object and point perpendicular with the base plane.

## Designing Learning Activities to Engage

Teachers can construct the tasks by dynamic geometry software which are not possible with paper-and-pencil technology. Furthermore they can design more interactive and interesting activities with 3D geometry software (both Euclidean and co-ordinate).the designer of such activities must be aware of the complexity of the images on-screen, and the need for learners to orient themselves to a flat-screen representation of 3D. There may also be issues for users moving from 2D DGE to 3D software. For instance, in two dimensional dynamic geometry software , the perpendicular tool just produce a line or segment, while in Cabri 3D this tool produce a perpendicular plane to a line and perpendicular to a line is a plane. (Hoyles & Baptiste Lagrange, 2010).

Such new issues about using tools in 3dimesonal geometry software are just begin to research. Because these issues emerged while teachers and researchers started to use these software as a mediate the learners' understanding of geometry .for example, Accascina and Rogora (2006) found that Cabri 3D as a very effective for quickly introducing students 3D geometry and giving them enough intuitive support for understanding non trivial. Then they repeated the experiment of plane section with grade Eight students, who had not any pervious knowledge of three-dimensional geometry. They observed students enjoyed the activities and were able to grasp the main intuitive ideas. They suggested, teachers should be conscious about confusions and misconceptions which may arise when interpreting a Cabri 3D diagram. Otherwise student will face confusions in their minds (Accascina & Rogora, 2006).

Another example of study on using Cabri 3D task in learning geometry has done by Mackrell (2008).in this research she has found that students at Grade 7 and 8 students get highly motivated to use Cabri 3D to create their own structures. That structure was consisting of real-world objects. Overall, mathematics education has benefited from some useful connections between technology designers and users, perhaps no more so than in the area of geometry education.(Hoyles & Lagrange, 2009)

## Summary:

In this chapter Van Hiele theory as the main theoretical frame work with its characteristics and phases of learning discussed, then the related literature on van Hiele theory involving using dynamic geometry software highlighted. Subsequently relevant litrature on Cabri 3D that have been carried out have disseised, following by issues in designing learning activates.

All in all, The Van Hiele Model provides us with a unique learning theory that can be related to Geometry and other areas of mathematics as well. The hope is that teachers who understand the different levels of the van Hiele Model will be able to recognize the level their students are currently functioning at and adjust their teaching accordingly. At the same time, the van Hieles always professed that success is very much based on adequate teaching.