1000-0.4x^2=42x

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Solution for 1000-0.4x^2=42x equation:


Simplifying
1000 + -0.4x2 = 42x

Solving
1000 + -0.4x2 = 42x

Solving for variable 'x'.

Reorder the terms:
1000 + -42x + -0.4x2 = 42x + -42x

Combine like terms: 42x + -42x = 0
1000 + -42x + -0.4x2 = 0

Begin completing the square.  Divide all terms by
-0.4 the coefficient of the squared term: 

Divide each side by '-0.4'.
-2500 + 105x + x2 = 0

Move the constant term to the right:

Add '2500' to each side of the equation.
-2500 + 105x + 2500 + x2 = 0 + 2500

Reorder the terms:
-2500 + 2500 + 105x + x2 = 0 + 2500

Combine like terms: -2500 + 2500 = 0
0 + 105x + x2 = 0 + 2500
105x + x2 = 0 + 2500

Combine like terms: 0 + 2500 = 2500
105x + x2 = 2500

The x term is 105x.  Take half its coefficient (52.5).
Square it (2756.25) and add it to both sides.

Add '2756.25' to each side of the equation.
105x + 2756.25 + x2 = 2500 + 2756.25

Reorder the terms:
2756.25 + 105x + x2 = 2500 + 2756.25

Combine like terms: 2500 + 2756.25 = 5256.25
2756.25 + 105x + x2 = 5256.25

Factor a perfect square on the left side:
(x + 52.5)(x + 52.5) = 5256.25

Calculate the square root of the right side: 72.5

Break this problem into two subproblems by setting 
(x + 52.5) equal to 72.5 and -72.5.

Subproblem 1

x + 52.5 = 72.5 Simplifying x + 52.5 = 72.5 Reorder the terms: 52.5 + x = 72.5 Solving 52.5 + x = 72.5 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-52.5' to each side of the equation. 52.5 + -52.5 + x = 72.5 + -52.5 Combine like terms: 52.5 + -52.5 = 0.0 0.0 + x = 72.5 + -52.5 x = 72.5 + -52.5 Combine like terms: 72.5 + -52.5 = 20 x = 20 Simplifying x = 20

Subproblem 2

x + 52.5 = -72.5 Simplifying x + 52.5 = -72.5 Reorder the terms: 52.5 + x = -72.5 Solving 52.5 + x = -72.5 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-52.5' to each side of the equation. 52.5 + -52.5 + x = -72.5 + -52.5 Combine like terms: 52.5 + -52.5 = 0.0 0.0 + x = -72.5 + -52.5 x = -72.5 + -52.5 Combine like terms: -72.5 + -52.5 = -125 x = -125 Simplifying x = -125

Solution

The solution to the problem is based on the solutions from the subproblems. x = {20, -125}

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