Find the center and radius of a circle modeled by the equation x2 + y2 - 4x + 2y - 4 = 0 by completing the square

ANSWER

Center: (2,-1)

Radius: 3 units.

EXPLANATION

The given circle has equation:



We rearrange to get;



We add the square of half the coefficients of the linear terms to both sides of the equation as shown below:



Look out for the perfect squares on the left hand side .







By comparing to :



We have the center to be

(h,k)=(2,-1) and radius r=3.