You must have the following vocabulary written on your khan notes including this picture!
Diameter;A line segment through the center of a circle with endpoints on the circle; also, the length of such a segment.
Radius; A segment with one endpoint at the center of a circle and the other endpoint on the circle. The length of this segment is also called the radius. Circumference; The distance around a circle. The formula is Dπ (Diameter times pi) Area; A measure of the amount of a surface enclosed by a geometric figure. Area is usually measured in square units. The formula for a circle is r²π (Pi times radius squared) |