The distance of a point (x, y) from the center of the target (0, 0) can be calculated with sqrt(x*x + y *y)
(x, y)
(0, 0)
sqrt(x*x + y *y)
You can calculate the square root of x by raising it to the power of 1/2. In other words, sqrt(x) == pow(x, 0.5)
x
1/2
sqrt(x) == pow(x, 0.5)