x(3x+8)=390

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Solution for x(3x+8)=390 equation:


Simplifying
x(3x + 8) = 390

Reorder the terms:
x(8 + 3x) = 390
(8 * x + 3x * x) = 390
(8x + 3x2) = 390

Solving
8x + 3x2 = 390

Solving for variable 'x'.

Reorder the terms:
-390 + 8x + 3x2 = 390 + -390

Combine like terms: 390 + -390 = 0
-390 + 8x + 3x2 = 0

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

Divide each side by '3'.
-130 + 2.666666667x + x2 = 0

Move the constant term to the right:

Add '130' to each side of the equation.
-130 + 2.666666667x + 130 + x2 = 0 + 130

Reorder the terms:
-130 + 130 + 2.666666667x + x2 = 0 + 130

Combine like terms: -130 + 130 = 0
0 + 2.666666667x + x2 = 0 + 130
2.666666667x + x2 = 0 + 130

Combine like terms: 0 + 130 = 130
2.666666667x + x2 = 130

The x term is 2.666666667x.  Take half its coefficient (1.333333334).
Square it (1.777777780) and add it to both sides.

Add '1.777777780' to each side of the equation.
2.666666667x + 1.777777780 + x2 = 130 + 1.777777780

Reorder the terms:
1.777777780 + 2.666666667x + x2 = 130 + 1.777777780

Combine like terms: 130 + 1.777777780 = 131.77777778
1.777777780 + 2.666666667x + x2 = 131.77777778

Factor a perfect square on the left side:
(x + 1.333333334)(x + 1.333333334) = 131.77777778

Calculate the square root of the right side: 11.479450239

Break this problem into two subproblems by setting 
(x + 1.333333334) equal to 11.479450239 and -11.479450239.

Subproblem 1

x + 1.333333334 = 11.479450239 Simplifying x + 1.333333334 = 11.479450239 Reorder the terms: 1.333333334 + x = 11.479450239 Solving 1.333333334 + x = 11.479450239 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.333333334' to each side of the equation. 1.333333334 + -1.333333334 + x = 11.479450239 + -1.333333334 Combine like terms: 1.333333334 + -1.333333334 = 0.000000000 0.000000000 + x = 11.479450239 + -1.333333334 x = 11.479450239 + -1.333333334 Combine like terms: 11.479450239 + -1.333333334 = 10.146116905 x = 10.146116905 Simplifying x = 10.146116905

Subproblem 2

x + 1.333333334 = -11.479450239 Simplifying x + 1.333333334 = -11.479450239 Reorder the terms: 1.333333334 + x = -11.479450239 Solving 1.333333334 + x = -11.479450239 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.333333334' to each side of the equation. 1.333333334 + -1.333333334 + x = -11.479450239 + -1.333333334 Combine like terms: 1.333333334 + -1.333333334 = 0.000000000 0.000000000 + x = -11.479450239 + -1.333333334 x = -11.479450239 + -1.333333334 Combine like terms: -11.479450239 + -1.333333334 = -12.812783573 x = -12.812783573 Simplifying x = -12.812783573

Solution

The solution to the problem is based on the solutions from the subproblems. x = {10.146116905, -12.812783573}

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