(2x^2-x^2)= x^2
(1+7) = 8
X^2 + 8
The answer is C. If you use the pythagorean theorem,

, and connect the two points together at a right angle and pug in the lengths of the two lines to the equation then the answer should be C.
For example, exc. 15.
x + y = 10 and 6/x = 9/y; You need y!
=> x = 10 -y and 9x = 6y => 9(10-y) = 6y => 90 - 9y = 6y => 15y = 90 => y = 6.