Question 39797
The radius is the distance from the middle to one point on the circle, so use the formula for distance:
{{{d = sqrt((y - y)^2 + (x - x)^2)}}}
{{{d = sqrt((-6 - 0)^2 + (3 - 0)^2)}}}
{{{d = sqrt(45)}}}
The formula for the circle: {{{y^2 + x^2 = 45}}}