0=x^2-40x+800

Solution for 0=x^2-40x+800 equation:

Simplifying
0 = x2 + -40x + 800

Reorder the terms:
0 = 800 + -40x + x2

Solving
0 = 800 + -40x + x2

Solving for variable 'x'.

Combine like terms: 0 + -800 = -800
-800 + 40x + -1x2 = 800 + -40x + x2 + -800 + 40x + -1x2

Reorder the terms:
-800 + 40x + -1x2 = 800 + -800 + -40x + 40x + x2 + -1x2

Combine like terms: 800 + -800 = 0
-800 + 40x + -1x2 = 0 + -40x + 40x + x2 + -1x2
-800 + 40x + -1x2 = -40x + 40x + x2 + -1x2

Combine like terms: -40x + 40x = 0
-800 + 40x + -1x2 = 0 + x2 + -1x2
-800 + 40x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
-800 + 40x + -1x2 = 0

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

Divide each side by '-1'.
800 + -40x + x2 = 0

Move the constant term to the right:

Add '-800' to each side of the equation.
800 + -40x + -800 + x2 = 0 + -800

Reorder the terms:
800 + -800 + -40x + x2 = 0 + -800

Combine like terms: 800 + -800 = 0
0 + -40x + x2 = 0 + -800
-40x + x2 = 0 + -800

Combine like terms: 0 + -800 = -800
-40x + x2 = -800

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

Add '400' to each side of the equation.
-40x + 400 + x2 = -800 + 400

Reorder the terms:
400 + -40x + x2 = -800 + 400

Combine like terms: -800 + 400 = -400
400 + -40x + x2 = -400

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

Can't calculate square root of the right side.

The solution to this equation could not be determined.