x-(.8*x^2)=3600

Solution for x-(.8*x^2)=3600 equation:

Simplifying
x + -1(0.8x2) = 3600

Remove parenthesis around (0.8x2)
x + -1 * 0.8x2 = 3600

Multiply -1 * 0.8
x + -0.8x2 = 3600

Solving
x + -0.8x2 = 3600

Solving for variable 'x'.

Reorder the terms:
-3600 + x + -0.8x2 = 3600 + -3600

Combine like terms: 3600 + -3600 = 0
-3600 + x + -0.8x2 = 0

Begin completing the square.  Divide all terms by
-0.8 the coefficient of the squared term: 

Divide each side by '-0.8'.
4500 + -1.25x + x2 = 0

Move the constant term to the right:

Add '-4500' to each side of the equation.
4500 + -1.25x + -4500 + x2 = 0 + -4500

Reorder the terms:
4500 + -4500 + -1.25x + x2 = 0 + -4500

Combine like terms: 4500 + -4500 = 0
0 + -1.25x + x2 = 0 + -4500
-1.25x + x2 = 0 + -4500

Combine like terms: 0 + -4500 = -4500
-1.25x + x2 = -4500

The x term is x.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1.25x + 0.25 + x2 = -4500 + 0.25

Reorder the terms:
0.25 + -1.25x + x2 = -4500 + 0.25

Combine like terms: -4500 + 0.25 = -4499.75
0.25 + -1.25x + x2 = -4499.75

Factor a perfect square on the left side:
(x + 0.5)(x + 0.5) = -4499.75

Can't calculate square root of the right side.

The solution to this equation could not be determined.