2b^2+20b-91=0

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


Simplifying
2b2 + 20b + -91 = 0

Reorder the terms:
-91 + 20b + 2b2 = 0

Solving
-91 + 20b + 2b2 = 0

Solving for variable 'b'.

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

Divide each side by '2'.
-45.5 + 10b + b2 = 0

Move the constant term to the right:

Add '45.5' to each side of the equation.
-45.5 + 10b + 45.5 + b2 = 0 + 45.5

Reorder the terms:
-45.5 + 45.5 + 10b + b2 = 0 + 45.5

Combine like terms: -45.5 + 45.5 = 0.0
0.0 + 10b + b2 = 0 + 45.5
10b + b2 = 0 + 45.5

Combine like terms: 0 + 45.5 = 45.5
10b + b2 = 45.5

The b term is 10b.  Take half its coefficient (5).
Square it (25) and add it to both sides.

Add '25' to each side of the equation.
10b + 25 + b2 = 45.5 + 25

Reorder the terms:
25 + 10b + b2 = 45.5 + 25

Combine like terms: 45.5 + 25 = 70.5
25 + 10b + b2 = 70.5

Factor a perfect square on the left side:
(b + 5)(b + 5) = 70.5

Calculate the square root of the right side: 8.396427812

Break this problem into two subproblems by setting 
(b + 5) equal to 8.396427812 and -8.396427812.

Subproblem 1

b + 5 = 8.396427812 Simplifying b + 5 = 8.396427812 Reorder the terms: 5 + b = 8.396427812 Solving 5 + b = 8.396427812 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + b = 8.396427812 + -5 Combine like terms: 5 + -5 = 0 0 + b = 8.396427812 + -5 b = 8.396427812 + -5 Combine like terms: 8.396427812 + -5 = 3.396427812 b = 3.396427812 Simplifying b = 3.396427812

Subproblem 2

b + 5 = -8.396427812 Simplifying b + 5 = -8.396427812 Reorder the terms: 5 + b = -8.396427812 Solving 5 + b = -8.396427812 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + b = -8.396427812 + -5 Combine like terms: 5 + -5 = 0 0 + b = -8.396427812 + -5 b = -8.396427812 + -5 Combine like terms: -8.396427812 + -5 = -13.396427812 b = -13.396427812 Simplifying b = -13.396427812

Solution

The solution to the problem is based on the solutions from the subproblems. b = {3.396427812, -13.396427812}

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