In the right triangle shown, what is the cosine of angle c?

The cos(C) = 
we first need to find the actual lengths of the sides.. to do this we will use the Pythagorean theorem:
(x + 15)² + (x + 1)² = (x + 17)²  and now after simplifying both sides and moving everything to one side we get the following quadratic equation:
x² - 2x - 63 = 0 and solving by factoring we get solutions of x = 9 and x = -7, but x = -7 does not make sense in this problem. 

Using x = 9 we see the sides of the triangle are 10, 24, and 26
the cos(c) =  which is about 0.9231