Question

Which is an equation of a circle with center (2, -1) that passes through the point (3, 4)?

Answer 1

Equation of circle is (x - a)^2 + (y - b)^2 = r^2; where (a, b) is the center and r is the radius.
r^2 = (2 - 3)^2 + (-1 - 4)^2 = (-1)^2 + (-5)^2 = 1 + 25 = 26
Equation is (x - 2)^2 + (y + 1)^2 = 26