7=-0.4x(x-10)

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Solution for 7=-0.4x(x-10) equation:


Simplifying
7 = -0.4x(x + -10)

Reorder the terms:
7 = -0.4x(-10 + x)
7 = (-10 * -0.4x + x * -0.4x)
7 = (4x + -0.4x2)

Solving
7 = 4x + -0.4x2

Solving for variable 'x'.

Reorder the terms:
7 + -4x + 0.4x2 = 4x + -4x + -0.4x2 + 0.4x2

Combine like terms: 4x + -4x = 0
7 + -4x + 0.4x2 = 0 + -0.4x2 + 0.4x2
7 + -4x + 0.4x2 = -0.4x2 + 0.4x2

Combine like terms: -0.4x2 + 0.4x2 = 0.0
7 + -4x + 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'.
17.5 + -10x + x2 = 0

Move the constant term to the right:

Add '-17.5' to each side of the equation.
17.5 + -10x + -17.5 + x2 = 0 + -17.5

Reorder the terms:
17.5 + -17.5 + -10x + x2 = 0 + -17.5

Combine like terms: 17.5 + -17.5 = 0.0
0.0 + -10x + x2 = 0 + -17.5
-10x + x2 = 0 + -17.5

Combine like terms: 0 + -17.5 = -17.5
-10x + x2 = -17.5

The x term is -10x.  Take half its coefficient (-5).
Square it (25) and add it to both sides.

Add '25' to each side of the equation.
-10x + 25 + x2 = -17.5 + 25

Reorder the terms:
25 + -10x + x2 = -17.5 + 25

Combine like terms: -17.5 + 25 = 7.5
25 + -10x + x2 = 7.5

Factor a perfect square on the left side:
(x + -5)(x + -5) = 7.5

Calculate the square root of the right side: 2.738612788

Break this problem into two subproblems by setting 
(x + -5) equal to 2.738612788 and -2.738612788.

Subproblem 1

x + -5 = 2.738612788 Simplifying x + -5 = 2.738612788 Reorder the terms: -5 + x = 2.738612788 Solving -5 + x = 2.738612788 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '5' to each side of the equation. -5 + 5 + x = 2.738612788 + 5 Combine like terms: -5 + 5 = 0 0 + x = 2.738612788 + 5 x = 2.738612788 + 5 Combine like terms: 2.738612788 + 5 = 7.738612788 x = 7.738612788 Simplifying x = 7.738612788

Subproblem 2

x + -5 = -2.738612788 Simplifying x + -5 = -2.738612788 Reorder the terms: -5 + x = -2.738612788 Solving -5 + x = -2.738612788 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '5' to each side of the equation. -5 + 5 + x = -2.738612788 + 5 Combine like terms: -5 + 5 = 0 0 + x = -2.738612788 + 5 x = -2.738612788 + 5 Combine like terms: -2.738612788 + 5 = 2.261387212 x = 2.261387212 Simplifying x = 2.261387212

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.738612788, 2.261387212}

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