3x^2+8x=420

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Solution for 3x^2+8x=420 equation:


Simplifying
3x2 + 8x = 420

Reorder the terms:
8x + 3x2 = 420

Solving
8x + 3x2 = 420

Solving for variable 'x'.

Reorder the terms:
-420 + 8x + 3x2 = 420 + -420

Combine like terms: 420 + -420 = 0
-420 + 8x + 3x2 = 0

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

Divide each side by '3'.
-140 + 2.666666667x + x2 = 0

Move the constant term to the right:

Add '140' to each side of the equation.
-140 + 2.666666667x + 140 + x2 = 0 + 140

Reorder the terms:
-140 + 140 + 2.666666667x + x2 = 0 + 140

Combine like terms: -140 + 140 = 0
0 + 2.666666667x + x2 = 0 + 140
2.666666667x + x2 = 0 + 140

Combine like terms: 0 + 140 = 140
2.666666667x + x2 = 140

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 = 140 + 1.777777780

Reorder the terms:
1.777777780 + 2.666666667x + x2 = 140 + 1.777777780

Combine like terms: 140 + 1.777777780 = 141.77777778
1.777777780 + 2.666666667x + x2 = 141.77777778

Factor a perfect square on the left side:
(x + 1.333333334)(x + 1.333333334) = 141.77777778

Calculate the square root of the right side: 11.9070474

Break this problem into two subproblems by setting 
(x + 1.333333334) equal to 11.9070474 and -11.9070474.

Subproblem 1

x + 1.333333334 = 11.9070474 Simplifying x + 1.333333334 = 11.9070474 Reorder the terms: 1.333333334 + x = 11.9070474 Solving 1.333333334 + x = 11.9070474 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 = 11.9070474 + -1.333333334 Combine like terms: 1.333333334 + -1.333333334 = 0.000000000 0.000000000 + x = 11.9070474 + -1.333333334 x = 11.9070474 + -1.333333334 Combine like terms: 11.9070474 + -1.333333334 = 10.573714066 x = 10.573714066 Simplifying x = 10.573714066

Subproblem 2

x + 1.333333334 = -11.9070474 Simplifying x + 1.333333334 = -11.9070474 Reorder the terms: 1.333333334 + x = -11.9070474 Solving 1.333333334 + x = -11.9070474 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 = -11.9070474 + -1.333333334 Combine like terms: 1.333333334 + -1.333333334 = 0.000000000 0.000000000 + x = -11.9070474 + -1.333333334 x = -11.9070474 + -1.333333334 Combine like terms: -11.9070474 + -1.333333334 = -13.240380734 x = -13.240380734 Simplifying x = -13.240380734

Solution

The solution to the problem is based on the solutions from the subproblems. x = {10.573714066, -13.240380734}

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