y(40+-1y)=800

Solution for y(40+-1y)=800 equation:

Simplifying
y(40 + -1y) = 800
(40 * y + -1y * y) = 800
(40y + -1y2) = 800

Solving
40y + -1y2 = 800

Solving for variable 'y'.

Reorder the terms:
-800 + 40y + -1y2 = 800 + -800

Combine like terms: 800 + -800 = 0
-800 + 40y + -1y2 = 0

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

Divide each side by '-1'.
800 + -40y + y2 = 0

Move the constant term to the right:

Add '-800' to each side of the equation.
800 + -40y + -800 + y2 = 0 + -800

Reorder the terms:
800 + -800 + -40y + y2 = 0 + -800

Combine like terms: 800 + -800 = 0
0 + -40y + y2 = 0 + -800
-40y + y2 = 0 + -800

Combine like terms: 0 + -800 = -800
-40y + y2 = -800

The y term is -40y.  Take half its coefficient (-20).
Square it (400) and add it to both sides.

Add '400' to each side of the equation.
-40y + 400 + y2 = -800 + 400

Reorder the terms:
400 + -40y + y2 = -800 + 400

Combine like terms: -800 + 400 = -400
400 + -40y + y2 = -400

Factor a perfect square on the left side:
(y + -20)(y + -20) = -400

Can't calculate square root of the right side.

The solution to this equation could not be determined.