A. x2 + (x + 3)2 = (x + 6)2
How do we know which is the hypotenuse? It's the longest.
x2 + x2 + 6x + 9 = x2 + 12x + 36
x2 - 6x - 27 = 0
(x - 9)(x + 3) = 0
In order for the left side to equal 0, either x - 9 or x + 3 has to equal 0, right?
x - 9 = 0
x = 9
x + 3 = 0
x = -3
If we were just solving for x, this would be an answer, but distance is not negative.
B. 9 + 6 = 15