7x-2x(x-10)=40

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Solution for 7x-2x(x-10)=40 equation:


Simplifying
7x + -2x(x + -10) = 40

Reorder the terms:
7x + -2x(-10 + x) = 40
7x + (-10 * -2x + x * -2x) = 40
7x + (20x + -2x2) = 40

Combine like terms: 7x + 20x = 27x
27x + -2x2 = 40

Solving
27x + -2x2 = 40

Solving for variable 'x'.

Reorder the terms:
-40 + 27x + -2x2 = 40 + -40

Combine like terms: 40 + -40 = 0
-40 + 27x + -2x2 = 0

Begin completing the square.  Divide all terms by
-2 the coefficient of the squared term: 

Divide each side by '-2'.
20 + -13.5x + x2 = 0

Move the constant term to the right:

Add '-20' to each side of the equation.
20 + -13.5x + -20 + x2 = 0 + -20

Reorder the terms:
20 + -20 + -13.5x + x2 = 0 + -20

Combine like terms: 20 + -20 = 0
0 + -13.5x + x2 = 0 + -20
-13.5x + x2 = 0 + -20

Combine like terms: 0 + -20 = -20
-13.5x + x2 = -20

The x term is -13.5x.  Take half its coefficient (-6.75).
Square it (45.5625) and add it to both sides.

Add '45.5625' to each side of the equation.
-13.5x + 45.5625 + x2 = -20 + 45.5625

Reorder the terms:
45.5625 + -13.5x + x2 = -20 + 45.5625

Combine like terms: -20 + 45.5625 = 25.5625
45.5625 + -13.5x + x2 = 25.5625

Factor a perfect square on the left side:
(x + -6.75)(x + -6.75) = 25.5625

Calculate the square root of the right side: 5.055937104

Break this problem into two subproblems by setting 
(x + -6.75) equal to 5.055937104 and -5.055937104.

Subproblem 1

x + -6.75 = 5.055937104 Simplifying x + -6.75 = 5.055937104 Reorder the terms: -6.75 + x = 5.055937104 Solving -6.75 + x = 5.055937104 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '6.75' to each side of the equation. -6.75 + 6.75 + x = 5.055937104 + 6.75 Combine like terms: -6.75 + 6.75 = 0.00 0.00 + x = 5.055937104 + 6.75 x = 5.055937104 + 6.75 Combine like terms: 5.055937104 + 6.75 = 11.805937104 x = 11.805937104 Simplifying x = 11.805937104

Subproblem 2

x + -6.75 = -5.055937104 Simplifying x + -6.75 = -5.055937104 Reorder the terms: -6.75 + x = -5.055937104 Solving -6.75 + x = -5.055937104 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '6.75' to each side of the equation. -6.75 + 6.75 + x = -5.055937104 + 6.75 Combine like terms: -6.75 + 6.75 = 0.00 0.00 + x = -5.055937104 + 6.75 x = -5.055937104 + 6.75 Combine like terms: -5.055937104 + 6.75 = 1.694062896 x = 1.694062896 Simplifying x = 1.694062896

Solution

The solution to the problem is based on the solutions from the subproblems. x = {11.805937104, 1.694062896}

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