2x^2+8x-91=0

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


Simplifying
2x2 + 8x + -91 = 0

Reorder the terms:
-91 + 8x + 2x2 = 0

Solving
-91 + 8x + 2x2 = 0

Solving for variable 'x'.

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

Divide each side by '2'.
-45.5 + 4x + x2 = 0

Move the constant term to the right:

Add '45.5' to each side of the equation.
-45.5 + 4x + 45.5 + x2 = 0 + 45.5

Reorder the terms:
-45.5 + 45.5 + 4x + x2 = 0 + 45.5

Combine like terms: -45.5 + 45.5 = 0.0
0.0 + 4x + x2 = 0 + 45.5
4x + x2 = 0 + 45.5

Combine like terms: 0 + 45.5 = 45.5
4x + x2 = 45.5

The x term is 4x.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4x + 4 + x2 = 45.5 + 4

Reorder the terms:
4 + 4x + x2 = 45.5 + 4

Combine like terms: 45.5 + 4 = 49.5
4 + 4x + x2 = 49.5

Factor a perfect square on the left side:
(x + 2)(x + 2) = 49.5

Calculate the square root of the right side: 7.03562364

Break this problem into two subproblems by setting 
(x + 2) equal to 7.03562364 and -7.03562364.

Subproblem 1

x + 2 = 7.03562364 Simplifying x + 2 = 7.03562364 Reorder the terms: 2 + x = 7.03562364 Solving 2 + x = 7.03562364 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + x = 7.03562364 + -2 Combine like terms: 2 + -2 = 0 0 + x = 7.03562364 + -2 x = 7.03562364 + -2 Combine like terms: 7.03562364 + -2 = 5.03562364 x = 5.03562364 Simplifying x = 5.03562364

Subproblem 2

x + 2 = -7.03562364 Simplifying x + 2 = -7.03562364 Reorder the terms: 2 + x = -7.03562364 Solving 2 + x = -7.03562364 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + x = -7.03562364 + -2 Combine like terms: 2 + -2 = 0 0 + x = -7.03562364 + -2 x = -7.03562364 + -2 Combine like terms: -7.03562364 + -2 = -9.03562364 x = -9.03562364 Simplifying x = -9.03562364

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.03562364, -9.03562364}

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