b^2-2b-84=0

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Solution for b^2-2b-84=0 equation:


Simplifying
b2 + -2b + -84 = 0

Reorder the terms:
-84 + -2b + b2 = 0

Solving
-84 + -2b + b2 = 0

Solving for variable 'b'.

Begin completing the square.

Move the constant term to the right:

Add '84' to each side of the equation.
-84 + -2b + 84 + b2 = 0 + 84

Reorder the terms:
-84 + 84 + -2b + b2 = 0 + 84

Combine like terms: -84 + 84 = 0
0 + -2b + b2 = 0 + 84
-2b + b2 = 0 + 84

Combine like terms: 0 + 84 = 84
-2b + b2 = 84

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 = 84 + 1

Reorder the terms:
1 + -2b + b2 = 84 + 1

Combine like terms: 84 + 1 = 85
1 + -2b + b2 = 85

Factor a perfect square on the left side:
(b + -1)(b + -1) = 85

Calculate the square root of the right side: 9.219544457

Break this problem into two subproblems by setting 
(b + -1) equal to 9.219544457 and -9.219544457.

Subproblem 1

b + -1 = 9.219544457 Simplifying b + -1 = 9.219544457 Reorder the terms: -1 + b = 9.219544457 Solving -1 + b = 9.219544457 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 = 9.219544457 + 1 Combine like terms: -1 + 1 = 0 0 + b = 9.219544457 + 1 b = 9.219544457 + 1 Combine like terms: 9.219544457 + 1 = 10.219544457 b = 10.219544457 Simplifying b = 10.219544457

Subproblem 2

b + -1 = -9.219544457 Simplifying b + -1 = -9.219544457 Reorder the terms: -1 + b = -9.219544457 Solving -1 + b = -9.219544457 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 = -9.219544457 + 1 Combine like terms: -1 + 1 = 0 0 + b = -9.219544457 + 1 b = -9.219544457 + 1 Combine like terms: -9.219544457 + 1 = -8.219544457 b = -8.219544457 Simplifying b = -8.219544457

Solution

The solution to the problem is based on the solutions from the subproblems. b = {10.219544457, -8.219544457}

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