This research aims to describe the level of geometric thinking and geometric thinking processes of Junior High School students according to van Hiele's level of thinking on the topic of quadrilaterals. The qualitative approach is the research method used in this study through a case study method by testing the Van Hiele Geometry Test (VHGT) which was adapted from Usiskin's CDASSG and conducting interviews about the thinking process in the form of identifying, defining, and classifying which was adapted from the interview guide of Burger and Shaughnessy (1986). The subjects of this study were 297 grade VII and VIII students from two schools located in the Lembang sub-district. The results of the VHGT test showed that there were 81 students counting level 0 (visualization). The results showed that the students of class VII and VIII level 0 were as follows: 1) students were able to recognize the types of quadrangle but still affected by the prototype, 2) students were not able to classify quadrilaterals, and 3) overall description of the geometric thinking process level 0 in the form of identifying, defining, and classifying aspects according to van Hiele's thinking characteristics in general.

The ellipse can be transformed into a circle by dilating the coordinates of the ellipse relative to the x-axis and y-axis. Therefore, this study aimed to derive the formula for the equation of the perimeter of an ellipse by using the transformation of an ellipse to a circle. This transformation was arranged so that the perimeter of the ellipse was equal to the perimeter of the circle. The type of research was in the review of books, articles, and relevant research reports. The results showed that the ellipse can be transformed into a circle while maintaining its perimeter. So, the perimeter of the ellipse was the same as the perimeter of the circle.