How do you find the radius of a circle with a defined equation of x2 plus y2-12x plus 8y plus 43 equals 0?

Answer 1

First, complete the square: x^2 - 12x + __ and y^2 + 8y + __.

so we have x^2 - 12x + 36 = (x - 6)^2, and y^2 + 8y + 16 = (y + 4)^2.

36 + 16 = 52, so we need to add 9 to both sides [43 + 9 = 52].

so the equation is now: (x - 6)2 + (y + 4)2= 9 = 3 2, so the radius is 3.