Which number is a solution to 8<×(7-×)

1 answer

8 < x(7-x)
-x^2 + 7x - 8 > 0
x = (7±√17)/2
From what you know about parabolas, the part above the x-axis lies outside the roots, so
x < (7-√17)/2 or x > (7+√17)/2