# 2.4 Circles

**Properties of Circles • Tangent Secant Lines • Circumference Area • Circular Arcs Angles • Radian Measure of an Angle**

The next geometric figure we consider is the circle. *All points on a* **circle** *are at the same distance from a fixed point, the* **center** *of the circle*. *The distance from the center to a point on the circle is the* **radius** *of the circle*. *The distance between two points on the circle on a line through the center is the* **diameter.** Therefore, the diameter `d` is twice the radius `r`, or $d\hspace{0.17em}=\hspace{0.17em}2r\hspace{0.17em}.\hspace{0.17em}$ See Fig. 2.76.

There are also certain types of lines associated with a circle. `A` **chord** *is a line segment having its endpoints ...*

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