0=x^2+8x-91

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Solution for 0=x^2+8x-91 equation:


Simplifying
0 = x2 + 8x + -91

Reorder the terms:
0 = -91 + 8x + x2

Solving
0 = -91 + 8x + x2

Solving for variable 'x'.

Combine like terms: 0 + 91 = 91
91 + -8x + -1x2 = -91 + 8x + x2 + 91 + -8x + -1x2

Reorder the terms:
91 + -8x + -1x2 = -91 + 91 + 8x + -8x + x2 + -1x2

Combine like terms: -91 + 91 = 0
91 + -8x + -1x2 = 0 + 8x + -8x + x2 + -1x2
91 + -8x + -1x2 = 8x + -8x + x2 + -1x2

Combine like terms: 8x + -8x = 0
91 + -8x + -1x2 = 0 + x2 + -1x2
91 + -8x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
91 + -8x + -1x2 = 0

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

Divide each side by '-1'.
-91 + 8x + x2 = 0

Move the constant term to the right:

Add '91' to each side of the equation.
-91 + 8x + 91 + x2 = 0 + 91

Reorder the terms:
-91 + 91 + 8x + x2 = 0 + 91

Combine like terms: -91 + 91 = 0
0 + 8x + x2 = 0 + 91
8x + x2 = 0 + 91

Combine like terms: 0 + 91 = 91
8x + x2 = 91

The x term is 8x.  Take half its coefficient (4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
8x + 16 + x2 = 91 + 16

Reorder the terms:
16 + 8x + x2 = 91 + 16

Combine like terms: 91 + 16 = 107
16 + 8x + x2 = 107

Factor a perfect square on the left side:
(x + 4)(x + 4) = 107

Calculate the square root of the right side: 10.344080433

Break this problem into two subproblems by setting 
(x + 4) equal to 10.344080433 and -10.344080433.

Subproblem 1

x + 4 = 10.344080433 Simplifying x + 4 = 10.344080433 Reorder the terms: 4 + x = 10.344080433 Solving 4 + x = 10.344080433 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + x = 10.344080433 + -4 Combine like terms: 4 + -4 = 0 0 + x = 10.344080433 + -4 x = 10.344080433 + -4 Combine like terms: 10.344080433 + -4 = 6.344080433 x = 6.344080433 Simplifying x = 6.344080433

Subproblem 2

x + 4 = -10.344080433 Simplifying x + 4 = -10.344080433 Reorder the terms: 4 + x = -10.344080433 Solving 4 + x = -10.344080433 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + x = -10.344080433 + -4 Combine like terms: 4 + -4 = 0 0 + x = -10.344080433 + -4 x = -10.344080433 + -4 Combine like terms: -10.344080433 + -4 = -14.344080433 x = -14.344080433 Simplifying x = -14.344080433

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.344080433, -14.344080433}

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