Outside of polygons, circles stand as one of the most important figures in your geometry class. A circle is defined as the set of points a fixed distance - the radius - from a center point. These can be represented visually, which is most common, or algebraically by using the equation form of a circle that takes in a center point and a radius. These representations of circles tie into the different problems you'll solve including measurements, cyclical polygon problems, and secant/tangent line problems just to name a few. In geometry, you'll learn how to make calculations with circles, including using circles to solve problems about other shapes. Having trouble? Fiveable's free geometry guides are here to help!