4x^2+20x-91=0

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Solution for 4x^2+20x-91=0 equation:


Simplifying
4x2 + 20x + -91 = 0

Reorder the terms:
-91 + 20x + 4x2 = 0

Solving
-91 + 20x + 4x2 = 0

Solving for variable 'x'.

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

Divide each side by '4'.
-22.75 + 5x + x2 = 0

Move the constant term to the right:

Add '22.75' to each side of the equation.
-22.75 + 5x + 22.75 + x2 = 0 + 22.75

Reorder the terms:
-22.75 + 22.75 + 5x + x2 = 0 + 22.75

Combine like terms: -22.75 + 22.75 = 0.00
0.00 + 5x + x2 = 0 + 22.75
5x + x2 = 0 + 22.75

Combine like terms: 0 + 22.75 = 22.75
5x + x2 = 22.75

The x term is 5x.  Take half its coefficient (2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
5x + 6.25 + x2 = 22.75 + 6.25

Reorder the terms:
6.25 + 5x + x2 = 22.75 + 6.25

Combine like terms: 22.75 + 6.25 = 29
6.25 + 5x + x2 = 29

Factor a perfect square on the left side:
(x + 2.5)(x + 2.5) = 29

Calculate the square root of the right side: 5.385164807

Break this problem into two subproblems by setting 
(x + 2.5) equal to 5.385164807 and -5.385164807.

Subproblem 1

x + 2.5 = 5.385164807 Simplifying x + 2.5 = 5.385164807 Reorder the terms: 2.5 + x = 5.385164807 Solving 2.5 + x = 5.385164807 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + x = 5.385164807 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + x = 5.385164807 + -2.5 x = 5.385164807 + -2.5 Combine like terms: 5.385164807 + -2.5 = 2.885164807 x = 2.885164807 Simplifying x = 2.885164807

Subproblem 2

x + 2.5 = -5.385164807 Simplifying x + 2.5 = -5.385164807 Reorder the terms: 2.5 + x = -5.385164807 Solving 2.5 + x = -5.385164807 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + x = -5.385164807 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + x = -5.385164807 + -2.5 x = -5.385164807 + -2.5 Combine like terms: -5.385164807 + -2.5 = -7.885164807 x = -7.885164807 Simplifying x = -7.885164807

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.885164807, -7.885164807}

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