x^2+7x-91=0

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Solution for x^2+7x-91=0 equation:


Simplifying
x2 + 7x + -91 = 0

Reorder the terms:
-91 + 7x + x2 = 0

Solving
-91 + 7x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '91' to each side of the equation.
-91 + 7x + 91 + x2 = 0 + 91

Reorder the terms:
-91 + 91 + 7x + x2 = 0 + 91

Combine like terms: -91 + 91 = 0
0 + 7x + x2 = 0 + 91
7x + x2 = 0 + 91

Combine like terms: 0 + 91 = 91
7x + x2 = 91

The x term is 7x.  Take half its coefficient (3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
7x + 12.25 + x2 = 91 + 12.25

Reorder the terms:
12.25 + 7x + x2 = 91 + 12.25

Combine like terms: 91 + 12.25 = 103.25
12.25 + 7x + x2 = 103.25

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 103.25

Calculate the square root of the right side: 10.161200716

Break this problem into two subproblems by setting 
(x + 3.5) equal to 10.161200716 and -10.161200716.

Subproblem 1

x + 3.5 = 10.161200716 Simplifying x + 3.5 = 10.161200716 Reorder the terms: 3.5 + x = 10.161200716 Solving 3.5 + x = 10.161200716 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.5' to each side of the equation. 3.5 + -3.5 + x = 10.161200716 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = 10.161200716 + -3.5 x = 10.161200716 + -3.5 Combine like terms: 10.161200716 + -3.5 = 6.661200716 x = 6.661200716 Simplifying x = 6.661200716

Subproblem 2

x + 3.5 = -10.161200716 Simplifying x + 3.5 = -10.161200716 Reorder the terms: 3.5 + x = -10.161200716 Solving 3.5 + x = -10.161200716 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.5' to each side of the equation. 3.5 + -3.5 + x = -10.161200716 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = -10.161200716 + -3.5 x = -10.161200716 + -3.5 Combine like terms: -10.161200716 + -3.5 = -13.661200716 x = -13.661200716 Simplifying x = -13.661200716

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.661200716, -13.661200716}

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