3x^2+21x+20=0

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Solution for 3x^2+21x+20=0 equation:


Simplifying
3x2 + 21x + 20 = 0

Reorder the terms:
20 + 21x + 3x2 = 0

Solving
20 + 21x + 3x2 = 0

Solving for variable 'x'.

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

Divide each side by '3'.
6.666666667 + 7x + x2 = 0

Move the constant term to the right:

Add '-6.666666667' to each side of the equation.
6.666666667 + 7x + -6.666666667 + x2 = 0 + -6.666666667

Reorder the terms:
6.666666667 + -6.666666667 + 7x + x2 = 0 + -6.666666667

Combine like terms: 6.666666667 + -6.666666667 = 0.000000000
0.000000000 + 7x + x2 = 0 + -6.666666667
7x + x2 = 0 + -6.666666667

Combine like terms: 0 + -6.666666667 = -6.666666667
7x + x2 = -6.666666667

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 = -6.666666667 + 12.25

Reorder the terms:
12.25 + 7x + x2 = -6.666666667 + 12.25

Combine like terms: -6.666666667 + 12.25 = 5.583333333
12.25 + 7x + x2 = 5.583333333

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 5.583333333

Calculate the square root of the right side: 2.362907813

Break this problem into two subproblems by setting 
(x + 3.5) equal to 2.362907813 and -2.362907813.

Subproblem 1

x + 3.5 = 2.362907813 Simplifying x + 3.5 = 2.362907813 Reorder the terms: 3.5 + x = 2.362907813 Solving 3.5 + x = 2.362907813 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 = 2.362907813 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = 2.362907813 + -3.5 x = 2.362907813 + -3.5 Combine like terms: 2.362907813 + -3.5 = -1.137092187 x = -1.137092187 Simplifying x = -1.137092187

Subproblem 2

x + 3.5 = -2.362907813 Simplifying x + 3.5 = -2.362907813 Reorder the terms: 3.5 + x = -2.362907813 Solving 3.5 + x = -2.362907813 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 = -2.362907813 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = -2.362907813 + -3.5 x = -2.362907813 + -3.5 Combine like terms: -2.362907813 + -3.5 = -5.862907813 x = -5.862907813 Simplifying x = -5.862907813

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-1.137092187, -5.862907813}

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