Abstract

Trigonometry is an essential branch in mathematics education. It has been claimed that trigonometry students instructed through use of triangles will face difficulties in picturing the behavior of the trigonometric functions, and consequently, fail to apprehend them. This study elaborates on notions about the effects of dynamic images illustrating angle variation using an adjustable triangle tool to scaffold trigonometric reasoning. We demonstrate how the scaffolding tool can help students develop reasoning about trigonometric functions. Findings from interviews with non-formal education students showed that the adjustable triangle tool allowed students to better understand trigonometric ratios by means of visualization of the angle variation. As a consequence the students showed increased reasoning, leading to improvements in trigonometric understanding. Our findings suggest that students’ difficulties of relating the measured angle to a trigonometric function may be due to the use of a static triangle, which does not support imagination and does not provide students with an effective foundation for reasoning. In conclusion, we have reason to believe that our teaching tool may benefit trigonometry instructions.