If you are trying to solve a right-angle triangle with Hypotenuse being 10 and one other side being 8, then you can use Pythogaras's theorem to do that as follows:
10^=8^2 + c^2
100=64 + c^2
c^2=100 - 64
c^2=36 take the square root of both sides,
c=6-being the 3rd side.
