What is the standard form of the equation of a circle with r = 5; (h, k) = (-5, 2)?

1 Answer
Dec 9, 2015

(x+5)2+(y2)2=25

Explanation:

The standard form of the equation of a circle of radius r centered at the point (h,k) is (xh)2+(yk)2=r2.

This equation is reflecting the fact that such a circle consists of all points in the plane that are distance r from (h,k). If a point P has rectangular coordinates (x,y), then the distance between P and (h,k) is given by the distance formula (xh)2+(yk)2 (which itself comes from the Pythagorean Theorem).

Setting that equal to r and squaring both sides gives the equation (xh)2+(yk)2=r2.