What is the radius of a circle whose equation is x2 + y2 – 10x + 6y + 18 = 0?

You can do this by completing the square on x and y terms:

  x^ - 10x + y^2 + 6y + 18 = 0

  (x - 5)^2 -25 + (y + 3)^2 - 9 + 18 = 0

  (x - 5)^2  + (y + 3)^2 = -18 + 9 + 25  =  16

so radius = sqrt16  = 4 answer