Answer:
-7
Step-by-step explanation:
∠D = ∠B
2x² + 7 = x² - 8x
2x² - x² + 8x + 7 = 0
x² + 8x + 7 = 0
(x + 7)(x + 1) = 0
x = -7 or -1
For x = -7, we have
x² - 8x = 49 + 56 = 105
2x² + 7 = 2*49 + 7 = 105 Right, x = -7 is an answer
For x = -1, we have
x² - 8x = 1 + 8 = 9 < 90
In the diagram angle B is > 90, so x = -1 is not the answer.
