3x^2-15x-28=0

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Solution for 3x^2-15x-28=0 equation: 


Simplifying
3x2 + -15x + -28 = 0

Reorder the terms:
-28 + -15x + 3x2 = 0

Solving
-28 + -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'.
-9.333333333 + -5x + x2 = 0

Move the constant term to the right:

Add '9.333333333' to each side of the equation.
-9.333333333 + -5x + 9.333333333 + x2 = 0 + 9.333333333

Reorder the terms:
-9.333333333 + 9.333333333 + -5x + x2 = 0 + 9.333333333

Combine like terms: -9.333333333 + 9.333333333 = 0.000000000
0.000000000 + -5x + x2 = 0 + 9.333333333
-5x + x2 = 0 + 9.333333333

Combine like terms: 0 + 9.333333333 = 9.333333333
-5x + x2 = 9.333333333

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 = 9.333333333 + 6.25

Reorder the terms:
6.25 + -5x + x2 = 9.333333333 + 6.25

Combine like terms: 9.333333333 + 6.25 = 15.583333333
6.25 + -5x + x2 = 15.583333333

Factor a perfect square on the left side:
(x + -2.5)(x + -2.5) = 15.583333333

Calculate the square root of the right side: 3.947573094

Break this problem into two subproblems by setting 
(x + -2.5) equal to 3.947573094 and -3.947573094.


Subproblem 1
x + -2.5 = 3.947573094

Simplifying
x + -2.5 = 3.947573094

Reorder the terms:
-2.5 + x = 3.947573094

Solving
-2.5 + x = 3.947573094

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 = 3.947573094 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + x = 3.947573094 + 2.5
x = 3.947573094 + 2.5

Combine like terms: 3.947573094 + 2.5 = 6.447573094
x = 6.447573094

Simplifying
x = 6.447573094


Subproblem 2
x + -2.5 = -3.947573094

Simplifying
x + -2.5 = -3.947573094

Reorder the terms:
-2.5 + x = -3.947573094

Solving
-2.5 + x = -3.947573094

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 = -3.947573094 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + x = -3.947573094 + 2.5
x = -3.947573094 + 2.5

Combine like terms: -3.947573094 + 2.5 = -1.447573094
x = -1.447573094

Simplifying
x = -1.447573094


Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {6.447573094, -1.447573094}

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