3x^2+21x-4x=218

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Solution for 3x^2+21x-4x=218 equation:


Simplifying
3x2 + 21x + -4x = 218

Reorder the terms:
21x + -4x + 3x2 = 218

Combine like terms: 21x + -4x = 17x
17x + 3x2 = 218

Solving
17x + 3x2 = 218

Solving for variable 'x'.

Reorder the terms:
-218 + 17x + 3x2 = 218 + -218

Combine like terms: 218 + -218 = 0
-218 + 17x + 3x2 = 0

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

Divide each side by '3'.
-72.66666667 + 5.666666667x + x2 = 0

Move the constant term to the right:

Add '72.66666667' to each side of the equation.
-72.66666667 + 5.666666667x + 72.66666667 + x2 = 0 + 72.66666667

Reorder the terms:
-72.66666667 + 72.66666667 + 5.666666667x + x2 = 0 + 72.66666667

Combine like terms: -72.66666667 + 72.66666667 = 0.00000000
0.00000000 + 5.666666667x + x2 = 0 + 72.66666667
5.666666667x + x2 = 0 + 72.66666667

Combine like terms: 0 + 72.66666667 = 72.66666667
5.666666667x + x2 = 72.66666667

The x term is 5.666666667x.  Take half its coefficient (2.833333334).
Square it (8.027777782) and add it to both sides.

Add '8.027777782' to each side of the equation.
5.666666667x + 8.027777782 + x2 = 72.66666667 + 8.027777782

Reorder the terms:
8.027777782 + 5.666666667x + x2 = 72.66666667 + 8.027777782

Combine like terms: 72.66666667 + 8.027777782 = 80.694444452
8.027777782 + 5.666666667x + x2 = 80.694444452

Factor a perfect square on the left side:
(x + 2.833333334)(x + 2.833333334) = 80.694444452

Calculate the square root of the right side: 8.983008653

Break this problem into two subproblems by setting 
(x + 2.833333334) equal to 8.983008653 and -8.983008653.

Subproblem 1

x + 2.833333334 = 8.983008653 Simplifying x + 2.833333334 = 8.983008653 Reorder the terms: 2.833333334 + x = 8.983008653 Solving 2.833333334 + x = 8.983008653 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.833333334' to each side of the equation. 2.833333334 + -2.833333334 + x = 8.983008653 + -2.833333334 Combine like terms: 2.833333334 + -2.833333334 = 0.000000000 0.000000000 + x = 8.983008653 + -2.833333334 x = 8.983008653 + -2.833333334 Combine like terms: 8.983008653 + -2.833333334 = 6.149675319 x = 6.149675319 Simplifying x = 6.149675319

Subproblem 2

x + 2.833333334 = -8.983008653 Simplifying x + 2.833333334 = -8.983008653 Reorder the terms: 2.833333334 + x = -8.983008653 Solving 2.833333334 + x = -8.983008653 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.833333334' to each side of the equation. 2.833333334 + -2.833333334 + x = -8.983008653 + -2.833333334 Combine like terms: 2.833333334 + -2.833333334 = 0.000000000 0.000000000 + x = -8.983008653 + -2.833333334 x = -8.983008653 + -2.833333334 Combine like terms: -8.983008653 + -2.833333334 = -11.816341987 x = -11.816341987 Simplifying x = -11.816341987

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.149675319, -11.816341987}

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