-x-x(x-21)=5x+7

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Solution for -x-x(x-21)=5x+7 equation:


Simplifying
-1x + -1x(x + -21) = 5x + 7

Reorder the terms:
-1x + -1x(-21 + x) = 5x + 7
-1x + (-21 * -1x + x * -1x) = 5x + 7
-1x + (21x + -1x2) = 5x + 7

Combine like terms: -1x + 21x = 20x
20x + -1x2 = 5x + 7

Reorder the terms:
20x + -1x2 = 7 + 5x

Solving
20x + -1x2 = 7 + 5x

Solving for variable 'x'.

Reorder the terms:
-7 + 20x + -5x + -1x2 = 7 + 5x + -7 + -5x

Combine like terms: 20x + -5x = 15x
-7 + 15x + -1x2 = 7 + 5x + -7 + -5x

Reorder the terms:
-7 + 15x + -1x2 = 7 + -7 + 5x + -5x

Combine like terms: 7 + -7 = 0
-7 + 15x + -1x2 = 0 + 5x + -5x
-7 + 15x + -1x2 = 5x + -5x

Combine like terms: 5x + -5x = 0
-7 + 15x + -1x2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
7 + -15x + x2 = 0

Move the constant term to the right:

Add '-7' to each side of the equation.
7 + -15x + -7 + x2 = 0 + -7

Reorder the terms:
7 + -7 + -15x + x2 = 0 + -7

Combine like terms: 7 + -7 = 0
0 + -15x + x2 = 0 + -7
-15x + x2 = 0 + -7

Combine like terms: 0 + -7 = -7
-15x + x2 = -7

The x term is -15x.  Take half its coefficient (-7.5).
Square it (56.25) and add it to both sides.

Add '56.25' to each side of the equation.
-15x + 56.25 + x2 = -7 + 56.25

Reorder the terms:
56.25 + -15x + x2 = -7 + 56.25

Combine like terms: -7 + 56.25 = 49.25
56.25 + -15x + x2 = 49.25

Factor a perfect square on the left side:
(x + -7.5)(x + -7.5) = 49.25

Calculate the square root of the right side: 7.017834424

Break this problem into two subproblems by setting 
(x + -7.5) equal to 7.017834424 and -7.017834424.

Subproblem 1

x + -7.5 = 7.017834424 Simplifying x + -7.5 = 7.017834424 Reorder the terms: -7.5 + x = 7.017834424 Solving -7.5 + x = 7.017834424 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + x = 7.017834424 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = 7.017834424 + 7.5 x = 7.017834424 + 7.5 Combine like terms: 7.017834424 + 7.5 = 14.517834424 x = 14.517834424 Simplifying x = 14.517834424

Subproblem 2

x + -7.5 = -7.017834424 Simplifying x + -7.5 = -7.017834424 Reorder the terms: -7.5 + x = -7.017834424 Solving -7.5 + x = -7.017834424 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + x = -7.017834424 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = -7.017834424 + 7.5 x = -7.017834424 + 7.5 Combine like terms: -7.017834424 + 7.5 = 0.482165576 x = 0.482165576 Simplifying x = 0.482165576

Solution

The solution to the problem is based on the solutions from the subproblems. x = {14.517834424, 0.482165576}

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