Explanation:
x² - 32 = 4x
x² - 4x - 32 = 0
with a little bit experience we see immediately that this is
(x - 8)(x + 4) = 0
the positive x for this to be true is x = 8.
formally, the solution to a quadratic equation
ax² + bx + c = 0
is
x = (-b ± sqrt(b² - 4ac))/(2a)
in our case
x = (4 ± sqrt((-4)² - 4×1×-32))/(2×1) =
= (4 ± sqrt(16 + 128))/2 = (4 ± sqrt(144))/2 =
= (4 ± 12)/2 = 2 ± 6
x1 = 2 + 6 = 8
x2 = 2 - 6 = -4
we were right at the beginning.
the positive solution is x = 8.