2x^2+21x+18=0

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Solution for 2x^2+21x+18=0 equation:


Simplifying
2x2 + 21x + 18 = 0

Reorder the terms:
18 + 21x + 2x2 = 0

Solving
18 + 21x + 2x2 = 0

Solving for variable 'x'.

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

Divide each side by '2'.
9 + 10.5x + x2 = 0

Move the constant term to the right:

Add '-9' to each side of the equation.
9 + 10.5x + -9 + x2 = 0 + -9

Reorder the terms:
9 + -9 + 10.5x + x2 = 0 + -9

Combine like terms: 9 + -9 = 0
0 + 10.5x + x2 = 0 + -9
10.5x + x2 = 0 + -9

Combine like terms: 0 + -9 = -9
10.5x + x2 = -9

The x term is 10.5x.  Take half its coefficient (5.25).
Square it (27.5625) and add it to both sides.

Add '27.5625' to each side of the equation.
10.5x + 27.5625 + x2 = -9 + 27.5625

Reorder the terms:
27.5625 + 10.5x + x2 = -9 + 27.5625

Combine like terms: -9 + 27.5625 = 18.5625
27.5625 + 10.5x + x2 = 18.5625

Factor a perfect square on the left side:
(x + 5.25)(x + 5.25) = 18.5625

Calculate the square root of the right side: 4.308421985

Break this problem into two subproblems by setting 
(x + 5.25) equal to 4.308421985 and -4.308421985.

Subproblem 1

x + 5.25 = 4.308421985 Simplifying x + 5.25 = 4.308421985 Reorder the terms: 5.25 + x = 4.308421985 Solving 5.25 + x = 4.308421985 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5.25' to each side of the equation. 5.25 + -5.25 + x = 4.308421985 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = 4.308421985 + -5.25 x = 4.308421985 + -5.25 Combine like terms: 4.308421985 + -5.25 = -0.941578015 x = -0.941578015 Simplifying x = -0.941578015

Subproblem 2

x + 5.25 = -4.308421985 Simplifying x + 5.25 = -4.308421985 Reorder the terms: 5.25 + x = -4.308421985 Solving 5.25 + x = -4.308421985 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5.25' to each side of the equation. 5.25 + -5.25 + x = -4.308421985 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = -4.308421985 + -5.25 x = -4.308421985 + -5.25 Combine like terms: -4.308421985 + -5.25 = -9.558421985 x = -9.558421985 Simplifying x = -9.558421985

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.941578015, -9.558421985}

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