x^2+18x=-1

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Solution for x^2+18x=-1 equation:


Simplifying
x2 + 18x = -1

Reorder the terms:
18x + x2 = -1

Solving
18x + x2 = -1

Solving for variable 'x'.

Reorder the terms:
1 + 18x + x2 = -1 + 1

Combine like terms: -1 + 1 = 0
1 + 18x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-1' to each side of the equation.
1 + 18x + -1 + x2 = 0 + -1

Reorder the terms:
1 + -1 + 18x + x2 = 0 + -1

Combine like terms: 1 + -1 = 0
0 + 18x + x2 = 0 + -1
18x + x2 = 0 + -1

Combine like terms: 0 + -1 = -1
18x + x2 = -1

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

Add '81' to each side of the equation.
18x + 81 + x2 = -1 + 81

Reorder the terms:
81 + 18x + x2 = -1 + 81

Combine like terms: -1 + 81 = 80
81 + 18x + x2 = 80

Factor a perfect square on the left side:
(x + 9)(x + 9) = 80

Calculate the square root of the right side: 8.94427191

Break this problem into two subproblems by setting 
(x + 9) equal to 8.94427191 and -8.94427191.

Subproblem 1

x + 9 = 8.94427191 Simplifying x + 9 = 8.94427191 Reorder the terms: 9 + x = 8.94427191 Solving 9 + x = 8.94427191 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-9' to each side of the equation. 9 + -9 + x = 8.94427191 + -9 Combine like terms: 9 + -9 = 0 0 + x = 8.94427191 + -9 x = 8.94427191 + -9 Combine like terms: 8.94427191 + -9 = -0.05572809 x = -0.05572809 Simplifying x = -0.05572809

Subproblem 2

x + 9 = -8.94427191 Simplifying x + 9 = -8.94427191 Reorder the terms: 9 + x = -8.94427191 Solving 9 + x = -8.94427191 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-9' to each side of the equation. 9 + -9 + x = -8.94427191 + -9 Combine like terms: 9 + -9 = 0 0 + x = -8.94427191 + -9 x = -8.94427191 + -9 Combine like terms: -8.94427191 + -9 = -17.94427191 x = -17.94427191 Simplifying x = -17.94427191

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.05572809, -17.94427191}

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