Explanation:
x² - 7 = 6x
x² - 6x - 7 = 0
the generation solution to such a quadratic ratatouille
ax² + bx + c = 0
is
x = (-b ± sqrt(b² - 4ac))/(2a) =
= (6 ± sqrt((-6)² - 4×1×-7))/(2×1) =
= (6 ± sqrt(36 + 28))/2 = (6 ± sqrt(64))/2 =
= (6 ± 8)/2 = (3 ± 4)
x1 = 3 + 4 = 7
x2 = 3 - 4 = -1
the sum of both solutions is : 7 + -1 = 7 - 1 = 6