b^2-5b-42=0

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Solution for b^2-5b-42=0 equation:


Simplifying
b2 + -5b + -42 = 0

Reorder the terms:
-42 + -5b + b2 = 0

Solving
-42 + -5b + b2 = 0

Solving for variable 'b'.

Begin completing the square.

Move the constant term to the right:

Add '42' to each side of the equation.
-42 + -5b + 42 + b2 = 0 + 42

Reorder the terms:
-42 + 42 + -5b + b2 = 0 + 42

Combine like terms: -42 + 42 = 0
0 + -5b + b2 = 0 + 42
-5b + b2 = 0 + 42

Combine like terms: 0 + 42 = 42
-5b + b2 = 42

The b term is -5b.  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.
-5b + 6.25 + b2 = 42 + 6.25

Reorder the terms:
6.25 + -5b + b2 = 42 + 6.25

Combine like terms: 42 + 6.25 = 48.25
6.25 + -5b + b2 = 48.25

Factor a perfect square on the left side:
(b + -2.5)(b + -2.5) = 48.25

Calculate the square root of the right side: 6.946221995

Break this problem into two subproblems by setting 
(b + -2.5) equal to 6.946221995 and -6.946221995.

Subproblem 1

b + -2.5 = 6.946221995 Simplifying b + -2.5 = 6.946221995 Reorder the terms: -2.5 + b = 6.946221995 Solving -2.5 + b = 6.946221995 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '2.5' to each side of the equation. -2.5 + 2.5 + b = 6.946221995 + 2.5 Combine like terms: -2.5 + 2.5 = 0.0 0.0 + b = 6.946221995 + 2.5 b = 6.946221995 + 2.5 Combine like terms: 6.946221995 + 2.5 = 9.446221995 b = 9.446221995 Simplifying b = 9.446221995

Subproblem 2

b + -2.5 = -6.946221995 Simplifying b + -2.5 = -6.946221995 Reorder the terms: -2.5 + b = -6.946221995 Solving -2.5 + b = -6.946221995 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '2.5' to each side of the equation. -2.5 + 2.5 + b = -6.946221995 + 2.5 Combine like terms: -2.5 + 2.5 = 0.0 0.0 + b = -6.946221995 + 2.5 b = -6.946221995 + 2.5 Combine like terms: -6.946221995 + 2.5 = -4.446221995 b = -4.446221995 Simplifying b = -4.446221995

Solution

The solution to the problem is based on the solutions from the subproblems. b = {9.446221995, -4.446221995}

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