What theorem do we use to solve for a side of a right triangle?

I would believe you are talking about the Pythagorean Theorem:

In that case the formula is L^2 + L^2 = H^2.

If you have the hypotenuse it is:

H^2 - L^2 = L^2:

When solving, just substitute your lengths for each side of the triangle.

Note: This only works with right triangles.

f(2x−x2)=−3x2+6x−1

step-by-step explanation:

set up the composite function and evaluate.

f(2x−x2)=−3x2+6x−1