3x^2+9x-15.12=0

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Solution for 3x^2+9x-15.12=0 equation:


Simplifying
3x2 + 9x + -15.12 = 0

Reorder the terms:
-15.12 + 9x + 3x2 = 0

Solving
-15.12 + 9x + 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'.
-5.04 + 3x + x2 = 0

Move the constant term to the right:

Add '5.04' to each side of the equation.
-5.04 + 3x + 5.04 + x2 = 0 + 5.04

Reorder the terms:
-5.04 + 5.04 + 3x + x2 = 0 + 5.04

Combine like terms: -5.04 + 5.04 = 0.00
0.00 + 3x + x2 = 0 + 5.04
3x + x2 = 0 + 5.04

Combine like terms: 0 + 5.04 = 5.04
3x + x2 = 5.04

The x term is 3x.  Take half its coefficient (1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
3x + 2.25 + x2 = 5.04 + 2.25

Reorder the terms:
2.25 + 3x + x2 = 5.04 + 2.25

Combine like terms: 5.04 + 2.25 = 7.29
2.25 + 3x + x2 = 7.29

Factor a perfect square on the left side:
(x + 1.5)(x + 1.5) = 7.29

Calculate the square root of the right side: 2.7

Break this problem into two subproblems by setting 
(x + 1.5) equal to 2.7 and -2.7.

Subproblem 1

x + 1.5 = 2.7 Simplifying x + 1.5 = 2.7 Reorder the terms: 1.5 + x = 2.7 Solving 1.5 + x = 2.7 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.5' to each side of the equation. 1.5 + -1.5 + x = 2.7 + -1.5 Combine like terms: 1.5 + -1.5 = 0.0 0.0 + x = 2.7 + -1.5 x = 2.7 + -1.5 Combine like terms: 2.7 + -1.5 = 1.2 x = 1.2 Simplifying x = 1.2

Subproblem 2

x + 1.5 = -2.7 Simplifying x + 1.5 = -2.7 Reorder the terms: 1.5 + x = -2.7 Solving 1.5 + x = -2.7 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.5' to each side of the equation. 1.5 + -1.5 + x = -2.7 + -1.5 Combine like terms: 1.5 + -1.5 = 0.0 0.0 + x = -2.7 + -1.5 x = -2.7 + -1.5 Combine like terms: -2.7 + -1.5 = -4.2 x = -4.2 Simplifying x = -4.2

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.2, -4.2}

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