2b^2+2b=91

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Solution for 2b^2+2b=91 equation:


Simplifying
2b2 + 2b = 91

Reorder the terms:
2b + 2b2 = 91

Solving
2b + 2b2 = 91

Solving for variable 'b'.

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

Combine like terms: 91 + -91 = 0
-91 + 2b + 2b2 = 0

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

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

Move the constant term to the right:

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

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

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

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

The b term is b.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
 + 0.25 + b2 = 45.5 + 0.25

Combine like terms:  + 0.25 = 1.25
1.25 + b2 = 45.5 + 0.25

Combine like terms: 45.5 + 0.25 = 45.75
1.25 + b2 = 45.75

Factor a perfect square on the left side:
(b + 0.5)(b + 0.5) = 45.75

Calculate the square root of the right side: 6.763874629

Break this problem into two subproblems by setting 
(b + 0.5) equal to 6.763874629 and -6.763874629.

Subproblem 1

b + 0.5 = 6.763874629 Simplifying b + 0.5 = 6.763874629 Reorder the terms: 0.5 + b = 6.763874629 Solving 0.5 + b = 6.763874629 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + b = 6.763874629 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + b = 6.763874629 + -0.5 b = 6.763874629 + -0.5 Combine like terms: 6.763874629 + -0.5 = 6.263874629 b = 6.263874629 Simplifying b = 6.263874629

Subproblem 2

b + 0.5 = -6.763874629 Simplifying b + 0.5 = -6.763874629 Reorder the terms: 0.5 + b = -6.763874629 Solving 0.5 + b = -6.763874629 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + b = -6.763874629 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + b = -6.763874629 + -0.5 b = -6.763874629 + -0.5 Combine like terms: -6.763874629 + -0.5 = -7.263874629 b = -7.263874629 Simplifying b = -7.263874629

Solution

The solution to the problem is based on the solutions from the subproblems. b = {6.263874629, -7.263874629}

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