What is the general form of the equation of a circle with center at (a, b) and radius of length m?

a.) x2 + y2 − 2ax − 2by + (a2 + b2 − m2) = 0
b.) x2 + y2 + 2ax + 2by + (a2 + b2 − m2) = 0
c.) x2 + y2 − 2ax − 2by + (a + b − m2) = 0
d.) x2 + y2 + 2ax + 2by + a2 + b2 = -m2

In the problem, it says that the center of the circle is at point (a,b) and has a radius of length m. In this case, the standard form of the circle is represented by the equation (x-h) ^2 + (y-k)^2 = r^2. Upon substitution, (x-a) ^2 + (y-b)^2 = m^2.This is equal to x2 - 2ax + a2 + y2 -2by + b2  = m2. The equation that is similar here is A