The equation of a circle is x2 + y2 + 6y = 7. What are the coordinates of the center and the length of the radius of the circle?
x^2 + y^2 + 6y = 7 complete the square on y
x^2 + y^2 + 6y + 9 = 7 + 9 simplify
x^2 + ( y + 3)^2 = 16 which we can write as
(x - 0)^2 + (y + 3)^2 = 16
So.......the center is (0, -3) and the radius is 4
