Find the exact length of the third side

You can use the Pythagorean theorem, a^2+b^2=c^2, to solve this.

b= square-root of (c^2)-(a^2)

b= square-root of (9^2)-(2^2)

b= 8.77 which in the exact form is square root of 77.

The answer would be quadratic trinomial

The variables should add up to equal 1