Geometry is different from the math that came before it because it requires you to remember definitions and know the difference between definitions and theorems. Also, you’ll be working with proofs for the first time! To get started, let’s look at the definition of a circle.

### A circle *C *of radius *r* and center *O *is the set of all points *P* in the plane such that |*OP*| = r.

Here’s an easier way of thinking about that: If you draw all the points that are the same distance (*r*) around one central point (*O*), eventually you’ll get a circle!

The cool thing about circles is that there’s really only one kind of circle. There might be differences in the length of the radii (plural for radiuses), but all circles will have the same **circumference** *C*=2π*r* and **area** A=π*r *(Tip: Circumference is the perimeter of a circle).

Read part 2 of this series for help with right triangles and how to use the Pythagorean Theorem and Pythagorean Triples. For additional help, check out Brightstorm Geometry.