The answer was pretty obvious but I had to go synthetic for a proof.
a^2 + c^2 = b^2 + d^2 = x^2 + (x-a)^2 + y^2 + (y-d)^2
The above is the relationship between the four lengths. Solving for d gives the requested solution:
d = sqrt(a^2 - b^2 + c^2)
Posted by Jer
on 2017-02-28 11:31:26