Question 963366
x^2 + (x + 4)^2 = 20^2
2x^2 + 8x + 16 = 400
x^2 + 4x + 8 = 200
x^2 + 4x - 192 = 0
(x + 16)(x - 12) = 0


x = 12 for the triangle to be right. Anything less makes it acute and anything more makes it obtuse, so the answer is D.