x^2+18x+21=0

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


Simplifying
x2 + 18x + 21 = 0

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

Solving
21 + 18x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + 18x + -21 + x2 = 0 + -21

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

Combine like terms: 21 + -21 = 0
0 + 18x + x2 = 0 + -21
18x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
18x + x2 = -21

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 = -21 + 81

Reorder the terms:
81 + 18x + x2 = -21 + 81

Combine like terms: -21 + 81 = 60
81 + 18x + x2 = 60

Factor a perfect square on the left side:
(x + 9)(x + 9) = 60

Calculate the square root of the right side: 7.745966692

Break this problem into two subproblems by setting 
(x + 9) equal to 7.745966692 and -7.745966692.

Subproblem 1

x + 9 = 7.745966692 Simplifying x + 9 = 7.745966692 Reorder the terms: 9 + x = 7.745966692 Solving 9 + x = 7.745966692 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 = 7.745966692 + -9 Combine like terms: 9 + -9 = 0 0 + x = 7.745966692 + -9 x = 7.745966692 + -9 Combine like terms: 7.745966692 + -9 = -1.254033308 x = -1.254033308 Simplifying x = -1.254033308

Subproblem 2

x + 9 = -7.745966692 Simplifying x + 9 = -7.745966692 Reorder the terms: 9 + x = -7.745966692 Solving 9 + x = -7.745966692 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 = -7.745966692 + -9 Combine like terms: 9 + -9 = 0 0 + x = -7.745966692 + -9 x = -7.745966692 + -9 Combine like terms: -7.745966692 + -9 = -16.745966692 x = -16.745966692 Simplifying x = -16.745966692

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-1.254033308, -16.745966692}

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