We want to solve
x(x + 8) = 256
Expand the left side.
x² + 8x = 256
Collect all terms on the left side.
x² + 8x - 256 = 0
Solve with the quadratic formula.
x = (1/2)*[-8 +/- √(8² -4*1*(-256)) ]
= -4 +/- (1/2)*√(1088)
= -4 +/- 16.4924
x = 12.4924, or x = -20.4924
Answer: x = 12.4924 or x = -20.4924
