4b^2+8b+7=42

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Solution for 4b^2+8b+7=42 equation:


Simplifying
4b2 + 8b + 7 = 42

Reorder the terms:
7 + 8b + 4b2 = 42

Solving
7 + 8b + 4b2 = 42

Solving for variable 'b'.

Reorder the terms:
7 + -42 + 8b + 4b2 = 42 + -42

Combine like terms: 7 + -42 = -35
-35 + 8b + 4b2 = 42 + -42

Combine like terms: 42 + -42 = 0
-35 + 8b + 4b2 = 0

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

Divide each side by '4'.
-8.75 + 2b + b2 = 0

Move the constant term to the right:

Add '8.75' to each side of the equation.
-8.75 + 2b + 8.75 + b2 = 0 + 8.75

Reorder the terms:
-8.75 + 8.75 + 2b + b2 = 0 + 8.75

Combine like terms: -8.75 + 8.75 = 0.00
0.00 + 2b + b2 = 0 + 8.75
2b + b2 = 0 + 8.75

Combine like terms: 0 + 8.75 = 8.75
2b + b2 = 8.75

The b term is 2b.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2b + 1 + b2 = 8.75 + 1

Reorder the terms:
1 + 2b + b2 = 8.75 + 1

Combine like terms: 8.75 + 1 = 9.75
1 + 2b + b2 = 9.75

Factor a perfect square on the left side:
(b + 1)(b + 1) = 9.75

Calculate the square root of the right side: 3.122498999

Break this problem into two subproblems by setting 
(b + 1) equal to 3.122498999 and -3.122498999.

Subproblem 1

b + 1 = 3.122498999 Simplifying b + 1 = 3.122498999 Reorder the terms: 1 + b = 3.122498999 Solving 1 + b = 3.122498999 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + b = 3.122498999 + -1 Combine like terms: 1 + -1 = 0 0 + b = 3.122498999 + -1 b = 3.122498999 + -1 Combine like terms: 3.122498999 + -1 = 2.122498999 b = 2.122498999 Simplifying b = 2.122498999

Subproblem 2

b + 1 = -3.122498999 Simplifying b + 1 = -3.122498999 Reorder the terms: 1 + b = -3.122498999 Solving 1 + b = -3.122498999 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + b = -3.122498999 + -1 Combine like terms: 1 + -1 = 0 0 + b = -3.122498999 + -1 b = -3.122498999 + -1 Combine like terms: -3.122498999 + -1 = -4.122498999 b = -4.122498999 Simplifying b = -4.122498999

Solution

The solution to the problem is based on the solutions from the subproblems. b = {2.122498999, -4.122498999}

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