The resultant force, r, is related to two concurrent forces, x and y, acting at right angles to one another, by the formula r^2 = x^2 = y^2 . rewrite the formula for y.

The two forces X and Y are acting at right angles which means the value of the resultant R is hypotenuse of the right triangle with X and Y as legs. This means R is governed by Pythagorean theorem: R^2 = X^2 + Y^2 Rewriting in terms of Y Y^2 = R^2 – X^2 Y = sqrt(R^2 – X^2)