b^2+18b-72=0

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Solution for b^2+18b-72=0 equation:


Simplifying
b2 + 18b + -72 = 0

Reorder the terms:
-72 + 18b + b2 = 0

Solving
-72 + 18b + b2 = 0

Solving for variable 'b'.

Begin completing the square.

Move the constant term to the right:

Add '72' to each side of the equation.
-72 + 18b + 72 + b2 = 0 + 72

Reorder the terms:
-72 + 72 + 18b + b2 = 0 + 72

Combine like terms: -72 + 72 = 0
0 + 18b + b2 = 0 + 72
18b + b2 = 0 + 72

Combine like terms: 0 + 72 = 72
18b + b2 = 72

The b term is 18b.  Take half its coefficient (9).
Square it (81) and add it to both sides.

Add '81' to each side of the equation.
18b + 81 + b2 = 72 + 81

Reorder the terms:
81 + 18b + b2 = 72 + 81

Combine like terms: 72 + 81 = 153
81 + 18b + b2 = 153

Factor a perfect square on the left side:
(b + 9)(b + 9) = 153

Calculate the square root of the right side: 12.369316877

Break this problem into two subproblems by setting 
(b + 9) equal to 12.369316877 and -12.369316877.

Subproblem 1

b + 9 = 12.369316877 Simplifying b + 9 = 12.369316877 Reorder the terms: 9 + b = 12.369316877 Solving 9 + b = 12.369316877 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-9' to each side of the equation. 9 + -9 + b = 12.369316877 + -9 Combine like terms: 9 + -9 = 0 0 + b = 12.369316877 + -9 b = 12.369316877 + -9 Combine like terms: 12.369316877 + -9 = 3.369316877 b = 3.369316877 Simplifying b = 3.369316877

Subproblem 2

b + 9 = -12.369316877 Simplifying b + 9 = -12.369316877 Reorder the terms: 9 + b = -12.369316877 Solving 9 + b = -12.369316877 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '-9' to each side of the equation. 9 + -9 + b = -12.369316877 + -9 Combine like terms: 9 + -9 = 0 0 + b = -12.369316877 + -9 b = -12.369316877 + -9 Combine like terms: -12.369316877 + -9 = -21.369316877 b = -21.369316877 Simplifying b = -21.369316877

Solution

The solution to the problem is based on the solutions from the subproblems. b = {3.369316877, -21.369316877}

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