x^2 + y^2 = 10
y = 3
The above equation represent the equation of a circle
x^2 + y^2 = r^2 --------- at the origin
(x - a)^2 + (y - b)^2 = r^2 -------- at points a and b
since y = 3
x = 0
r^2 = 10
we can find r by finding the squareroot of both sides
(0 , 3) and r = root of 10