"Their corresponding diagonals are equal" is the one conclusion among the following choices given in the question that is true about the quadrilaterals. The correct option among all the options that are given in the question is the first option. I hope that this is the answer that has actually come to your help.
Explanation: Think about it like your pluging in a number for x, like g(1) or g(x+1), but plug in the equation for f(x) g(f(x))= -(-8x^2 -5) -7 =8x^2 +5 -7 =8x^2 -2