15=2x^2+5x-9

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Solution for 15=2x^2+5x-9 equation:


Simplifying
15 = 2x2 + 5x + -9

Reorder the terms:
15 = -9 + 5x + 2x2

Solving
15 = -9 + 5x + 2x2

Solving for variable 'x'.

Combine like terms: 15 + 9 = 24
24 + -5x + -2x2 = -9 + 5x + 2x2 + 9 + -5x + -2x2

Reorder the terms:
24 + -5x + -2x2 = -9 + 9 + 5x + -5x + 2x2 + -2x2

Combine like terms: -9 + 9 = 0
24 + -5x + -2x2 = 0 + 5x + -5x + 2x2 + -2x2
24 + -5x + -2x2 = 5x + -5x + 2x2 + -2x2

Combine like terms: 5x + -5x = 0
24 + -5x + -2x2 = 0 + 2x2 + -2x2
24 + -5x + -2x2 = 2x2 + -2x2

Combine like terms: 2x2 + -2x2 = 0
24 + -5x + -2x2 = 0

Begin completing the square.  Divide all terms by
-2 the coefficient of the squared term: 

Divide each side by '-2'.
-12 + 2.5x + x2 = 0

Move the constant term to the right:

Add '12' to each side of the equation.
-12 + 2.5x + 12 + x2 = 0 + 12

Reorder the terms:
-12 + 12 + 2.5x + x2 = 0 + 12

Combine like terms: -12 + 12 = 0
0 + 2.5x + x2 = 0 + 12
2.5x + x2 = 0 + 12

Combine like terms: 0 + 12 = 12
2.5x + x2 = 12

The x term is 2.5x.  Take half its coefficient (1.25).
Square it (1.5625) and add it to both sides.

Add '1.5625' to each side of the equation.
2.5x + 1.5625 + x2 = 12 + 1.5625

Reorder the terms:
1.5625 + 2.5x + x2 = 12 + 1.5625

Combine like terms: 12 + 1.5625 = 13.5625
1.5625 + 2.5x + x2 = 13.5625

Factor a perfect square on the left side:
(x + 1.25)(x + 1.25) = 13.5625

Calculate the square root of the right side: 3.682729966

Break this problem into two subproblems by setting 
(x + 1.25) equal to 3.682729966 and -3.682729966.

Subproblem 1

x + 1.25 = 3.682729966 Simplifying x + 1.25 = 3.682729966 Reorder the terms: 1.25 + x = 3.682729966 Solving 1.25 + x = 3.682729966 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.25' to each side of the equation. 1.25 + -1.25 + x = 3.682729966 + -1.25 Combine like terms: 1.25 + -1.25 = 0.00 0.00 + x = 3.682729966 + -1.25 x = 3.682729966 + -1.25 Combine like terms: 3.682729966 + -1.25 = 2.432729966 x = 2.432729966 Simplifying x = 2.432729966

Subproblem 2

x + 1.25 = -3.682729966 Simplifying x + 1.25 = -3.682729966 Reorder the terms: 1.25 + x = -3.682729966 Solving 1.25 + x = -3.682729966 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.25' to each side of the equation. 1.25 + -1.25 + x = -3.682729966 + -1.25 Combine like terms: 1.25 + -1.25 = 0.00 0.00 + x = -3.682729966 + -1.25 x = -3.682729966 + -1.25 Combine like terms: -3.682729966 + -1.25 = -4.932729966 x = -4.932729966 Simplifying x = -4.932729966

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.432729966, -4.932729966}

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