3x^2+21x+12=0

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Solution for 3x^2+21x+12=0 equation: 


Simplifying
3x2 + 21x + 12 = 0

Reorder the terms:
12 + 21x + 3x2 = 0

Solving
12 + 21x + 3x2 = 0

Solving for variable 'x'.

Factor out the Greatest Common Factor (GCF), '3'.
3(4 + 7x + x2) = 0

Ignore the factor 3.

Subproblem 1
Set the factor '(4 + 7x + x2)' equal to zero and attempt to solve:

Simplifying
4 + 7x + x2 = 0

Solving
4 + 7x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-4' to each side of the equation.
4 + 7x + -4 + x2 = 0 + -4

Reorder the terms:
4 + -4 + 7x + x2 = 0 + -4

Combine like terms: 4 + -4 = 0
0 + 7x + x2 = 0 + -4
7x + x2 = 0 + -4

Combine like terms: 0 + -4 = -4
7x + x2 = -4

The x term is 7x.  Take half its coefficient (3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
7x + 12.25 + x2 = -4 + 12.25

Reorder the terms:
12.25 + 7x + x2 = -4 + 12.25

Combine like terms: -4 + 12.25 = 8.25
12.25 + 7x + x2 = 8.25

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 8.25

Calculate the square root of the right side: 2.872281323

Break this problem into two subproblems by setting 
(x + 3.5) equal to 2.872281323 and -2.872281323.


Subproblem 1
x + 3.5 = 2.872281323

Simplifying
x + 3.5 = 2.872281323

Reorder the terms:
3.5 + x = 2.872281323

Solving
3.5 + x = 2.872281323

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-3.5' to each side of the equation.
3.5 + -3.5 + x = 2.872281323 + -3.5

Combine like terms: 3.5 + -3.5 = 0.0
0.0 + x = 2.872281323 + -3.5
x = 2.872281323 + -3.5

Combine like terms: 2.872281323 + -3.5 = -0.627718677
x = -0.627718677

Simplifying
x = -0.627718677


Subproblem 2
x + 3.5 = -2.872281323

Simplifying
x + 3.5 = -2.872281323

Reorder the terms:
3.5 + x = -2.872281323

Solving
3.5 + x = -2.872281323

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-3.5' to each side of the equation.
3.5 + -3.5 + x = -2.872281323 + -3.5

Combine like terms: 3.5 + -3.5 = 0.0
0.0 + x = -2.872281323 + -3.5
x = -2.872281323 + -3.5

Combine like terms: -2.872281323 + -3.5 = -6.372281323
x = -6.372281323

Simplifying
x = -6.372281323


Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {-0.627718677, -6.372281323}
Solution
x = {-0.627718677, -6.372281323}

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