rs+h^2=1 for h

[math_celebrity]

rs+h^2=1 for h

Subtract rs from each side to isolate h:
rs - rs + h^2 = 1 - rs

Cancel the rs on the left side:
h^2 = 1 - rs

Take the square root of each side:
sqrt(h^2) = sqrt(1 - rs)
h = +- sqrt(1 -rs)