An analytic geometry question + algebra We have a Cartesian coordinate system with the points M (a,b) Q (4,2) and P (x,y) but I don't think you need P to solve this one, only M and Q. M is the middle of a circle with a radius r, and Q is a point on the circle (P is too, that's why I think P is redundant). What is the equation of this circle?
I thought it was: (4-a)^2 + (2-b)^2 = r^2
Is this correct my friends?

$(4-a)^2 + (2-b)^2 = r^2$, so you have to take the square root of the LHS:
$r = \sqrt ((4-a)^2 + (2-b)^2)$
