Question

If the point (1, 5) lies on a circle whose center is at the origin, what is the equation of the circle?
x2 + y2 = 26
x2 + y2 = 16
x2 + y2 = 13
x2 + y2 = 11

Answer 1

r^2 = 5^2 +1 =26

so
x2 + y2 = 26

Answer 2

the first one ... as it satisfies the point on its eqn