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In this study, we administrated dynamic geometry activities which provide students opportunities to explore and estimate geometric figures to connect measurement estimation with geometry. The aim of the study is to investigate effects of using dynamic geometry activities on eighth graders' achievement levels and estimation performances in triangles. The study was designed a quantitative research design. A pretestposttest experimental study was employed to investigate using dynamic geometry activities on eighth grade students' achievement level and estimation performance in triangles. Participants were 63 eighth graders. The participants' ages vary between 13 and 14 years. Since the school is a public school, it contains students at nearly every socio-economic level. Experimental group consists of 32 students and comparison group consists of 31 students. Dynamic geometry supported instruction and traditional instruction methods were used in experimental and comparison groups, respectively. The results revealed that teaching triangles with instruction supported by dynamic geometry activities increased eighth graders' performance in triangles. In addition, the instruction supported by dynamic geometry activities had significant effects on eighth graders' estimation performances in triangles. Using dynamic geometry activities provides students experiences about conceptual bases of the relations in triangles. Therefore, students who take a dynamic geometry instruction make better estimations than those who did not take.

Abstract-In this research; a problem situation, which requires the ability of thinking in three dimensions, was developed by the researchers. As the purpose of this paper is producing a modeling task suggestion, the problem was visualized and analyzed in GeoGebra3D environment. Then visual solution was also been supported by algebraic approach. So, the capability of creating the relationship between geometric and algebraic representations in GeoGebra was also presented in 3D sense.

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