Circles are really cool shapes in geometry! Here are some important terms to know:

• Radius: This is the distance from the center of the circle to any point on the edge. You can think of the radius as the “arm” reaching out from the middle. We usually write it as $r$.

• Diameter: The diameter is twice as long as the radius. So, if you know the radius, you can find the diameter with the equation $d = 2r$. The diameter is the longest distance across the circle, going straight through the center.

• Circumference: This is like the “fence” around the circle. It tells us how long the edge of the circle is. You can figure out the circumference using this formula: $C = \pi d$ or $C = 2\pi r$.

When you understand these basics, it makes it easier to learn more complex things about circles!