Question

What is the general form of the equation of a circle with center at (a, b) and radius of length m?
x2 + y2 − 2ax − 2by + (a2 + b2 − m2) = 0
x2 + y2 + 2ax + 2by + (a2 + b2 − m2) = 0
x2 + y2 − 2ax − 2by + (a + b − m2) = 0
x2 + y2 + 2ax + 2by + a2 + b2 = -m2

Answer 1

this:
x2 + y2 − 2ax − 2by + (a2 + b2 − m2) = 0

because:
\[(x-a)^{2}+(y-a)^{2}=m^{2} => x^{2}-2ax+a^{2}+y^{2}-2by+b^{2}=m^{2}\]