125=20x-.4x^2

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Solution for 125=20x-.4x^2 equation:


Simplifying
125 = 20x + -0.4x2

Solving
125 = 20x + -0.4x2

Solving for variable 'x'.

Reorder the terms:
125 + -20x + 0.4x2 = 20x + -20x + -0.4x2 + 0.4x2

Combine like terms: 20x + -20x = 0
125 + -20x + 0.4x2 = 0 + -0.4x2 + 0.4x2
125 + -20x + 0.4x2 = -0.4x2 + 0.4x2

Combine like terms: -0.4x2 + 0.4x2 = 0.0
125 + -20x + 0.4x2 = 0.0

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

Divide each side by '0.4'.
312.5 + -50x + x2 = 0

Move the constant term to the right:

Add '-312.5' to each side of the equation.
312.5 + -50x + -312.5 + x2 = 0 + -312.5

Reorder the terms:
312.5 + -312.5 + -50x + x2 = 0 + -312.5

Combine like terms: 312.5 + -312.5 = 0.0
0.0 + -50x + x2 = 0 + -312.5
-50x + x2 = 0 + -312.5

Combine like terms: 0 + -312.5 = -312.5
-50x + x2 = -312.5

The x term is -50x.  Take half its coefficient (-25).
Square it (625) and add it to both sides.

Add '625' to each side of the equation.
-50x + 625 + x2 = -312.5 + 625

Reorder the terms:
625 + -50x + x2 = -312.5 + 625

Combine like terms: -312.5 + 625 = 312.5
625 + -50x + x2 = 312.5

Factor a perfect square on the left side:
(x + -25)(x + -25) = 312.5

Calculate the square root of the right side: 17.67766953

Break this problem into two subproblems by setting 
(x + -25) equal to 17.67766953 and -17.67766953.

Subproblem 1

x + -25 = 17.67766953 Simplifying x + -25 = 17.67766953 Reorder the terms: -25 + x = 17.67766953 Solving -25 + x = 17.67766953 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '25' to each side of the equation. -25 + 25 + x = 17.67766953 + 25 Combine like terms: -25 + 25 = 0 0 + x = 17.67766953 + 25 x = 17.67766953 + 25 Combine like terms: 17.67766953 + 25 = 42.67766953 x = 42.67766953 Simplifying x = 42.67766953

Subproblem 2

x + -25 = -17.67766953 Simplifying x + -25 = -17.67766953 Reorder the terms: -25 + x = -17.67766953 Solving -25 + x = -17.67766953 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '25' to each side of the equation. -25 + 25 + x = -17.67766953 + 25 Combine like terms: -25 + 25 = 0 0 + x = -17.67766953 + 25 x = -17.67766953 + 25 Combine like terms: -17.67766953 + 25 = 7.32233047 x = 7.32233047 Simplifying x = 7.32233047

Solution

The solution to the problem is based on the solutions from the subproblems. x = {42.67766953, 7.32233047}

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