1.8 Circles

A circle is a set of points in the xy-plane that are a fixed distance r from a fixed point (h,k). The fixed distance is called the radius, and the fixed point (h,k) is called the center of the circle. y (x, y) r (h, k) x

The standard form of an equation of a circle with radius r and center (h,k) is

Graph ( ) x y + - = 1 3 16 2

y (-1, 7) (3,3) (-5, 3) (-1,3) x (-1, -1)

The general form of the equation of a circle

Find the center and the radius of First group terms:

Add appropriate terms to complete the squares for x and for y.