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Abstract: The circle is the set of points that are equidistant to a particular point called the center. The concept of a circle is one of the most important concepts in mathematics. Some problems in daily life can be solved with the concept of a circle. Representations made by students can give an idea of the level of understanding that has been achieved by these students. Representation can be used as a tool to solve problems. Representations of number include objects, actions, pictures, symbols, and words. Representations are useful tools that support mathematical reasoning, enable mathematical communication, and convey mathematical thought. Students use representations to support understanding when they are solving mathematical problems or learning new mathematical concepts. Various representations that arise when a student is given a matter of the equation of a circle. Some students when given a problem to determine the equation of a circle that is known to the center and fingers 1. Make a sketch of a circle image on cartesian coordinates then determine the equation of circle 2. Without drawing directly determine the equation of a circle by substituting the center and radius of the formula (x-a)^2+(y-b)^2=r^2.. Students who sketched a circle image first tend to have a better understanding than students who directly substitute into the general form of the circle equation.