Misconception of triangle concept through epistemological mathematics belief

Triangle topics have been studied since preschool. However, there are still pre-services teachers who do not understand the triangle concept. This descriptive qualitative study aims to trace the understanding of the base and the altitude of the triangle concept. A total of 30 pre-service teachers of elementary school were assigned to solve the problem on the triangle topic. Futhermore, an interview was conducted to explore the subject's understanding of the triangle concept. The results revealed that the base of the triangle was understood as the horizontal side of the triangle, located at the bottom or one of the longest sides of the triangle. The altitude of the triangle was an vertical side of the right triangle or a distance between the base of the triangle and the vertex before it. Misconception of triangle concept was due to the given examples of triangles limited to the right triangle, the equilateral triangle, and the isosceles of triangle. Varying samples which represent all types of triangles and varied problem will build the understanding concept of the base and altitude of the triangle correctly.