3x^2+15x-8.1=0

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Solution for 3x^2+15x-8.1=0 equation: 


Simplifying
3x2 + 15x + -8.1 = 0

Reorder the terms:
-8.1 + 15x + 3x2 = 0

Solving
-8.1 + 15x + 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'.
-2.7 + 5x + x2 = 0

Move the constant term to the right:

Add '2.7' to each side of the equation.
-2.7 + 5x + 2.7 + x2 = 0 + 2.7

Reorder the terms:
-2.7 + 2.7 + 5x + x2 = 0 + 2.7

Combine like terms: -2.7 + 2.7 = 0.0
0.0 + 5x + x2 = 0 + 2.7
5x + x2 = 0 + 2.7

Combine like terms: 0 + 2.7 = 2.7
5x + x2 = 2.7

The x term is 5x.  Take half its coefficient (2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
5x + 6.25 + x2 = 2.7 + 6.25

Reorder the terms:
6.25 + 5x + x2 = 2.7 + 6.25

Combine like terms: 2.7 + 6.25 = 8.95
6.25 + 5x + x2 = 8.95

Factor a perfect square on the left side:
(x + 2.5)(x + 2.5) = 8.95

Calculate the square root of the right side: 2.99165506

Break this problem into two subproblems by setting 
(x + 2.5) equal to 2.99165506 and -2.99165506.


Subproblem 1
x + 2.5 = 2.99165506

Simplifying
x + 2.5 = 2.99165506

Reorder the terms:
2.5 + x = 2.99165506

Solving
2.5 + x = 2.99165506

Solving for variable 'x'.

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

Add '-2.5' to each side of the equation.
2.5 + -2.5 + x = 2.99165506 + -2.5

Combine like terms: 2.5 + -2.5 = 0.0
0.0 + x = 2.99165506 + -2.5
x = 2.99165506 + -2.5

Combine like terms: 2.99165506 + -2.5 = 0.49165506
x = 0.49165506

Simplifying
x = 0.49165506


Subproblem 2
x + 2.5 = -2.99165506

Simplifying
x + 2.5 = -2.99165506

Reorder the terms:
2.5 + x = -2.99165506

Solving
2.5 + x = -2.99165506

Solving for variable 'x'.

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

Add '-2.5' to each side of the equation.
2.5 + -2.5 + x = -2.99165506 + -2.5

Combine like terms: 2.5 + -2.5 = 0.0
0.0 + x = -2.99165506 + -2.5
x = -2.99165506 + -2.5

Combine like terms: -2.99165506 + -2.5 = -5.49165506
x = -5.49165506

Simplifying
x = -5.49165506


Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {0.49165506, -5.49165506}

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