y(8-y)=128

Solution for y(8-y)=128 equation:

Simplifying
y(8 + -1y) = 128
(8 * y + -1y * y) = 128
(8y + -1y2) = 128

Solving
8y + -1y2 = 128

Solving for variable 'y'.

Reorder the terms:
-128 + 8y + -1y2 = 128 + -128

Combine like terms: 128 + -128 = 0
-128 + 8y + -1y2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
128 + -8y + y2 = 0

Move the constant term to the right:

Add '-128' to each side of the equation.
128 + -8y + -128 + y2 = 0 + -128

Reorder the terms:
128 + -128 + -8y + y2 = 0 + -128

Combine like terms: 128 + -128 = 0
0 + -8y + y2 = 0 + -128
-8y + y2 = 0 + -128

Combine like terms: 0 + -128 = -128
-8y + y2 = -128

The y term is -8y.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8y + 16 + y2 = -128 + 16

Reorder the terms:
16 + -8y + y2 = -128 + 16

Combine like terms: -128 + 16 = -112
16 + -8y + y2 = -112

Factor a perfect square on the left side:
(y + -4)(y + -4) = -112

Can't calculate square root of the right side.

The solution to this equation could not be determined.