2x^2+21x+15=0

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Solution for 2x^2+21x+15=0 equation:


Simplifying
2x2 + 21x + 15 = 0

Reorder the terms:
15 + 21x + 2x2 = 0

Solving
15 + 21x + 2x2 = 0

Solving for variable 'x'.

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

Divide each side by '2'.
7.5 + 10.5x + x2 = 0

Move the constant term to the right:

Add '-7.5' to each side of the equation.
7.5 + 10.5x + -7.5 + x2 = 0 + -7.5

Reorder the terms:
7.5 + -7.5 + 10.5x + x2 = 0 + -7.5

Combine like terms: 7.5 + -7.5 = 0.0
0.0 + 10.5x + x2 = 0 + -7.5
10.5x + x2 = 0 + -7.5

Combine like terms: 0 + -7.5 = -7.5
10.5x + x2 = -7.5

The x term is 10.5x.  Take half its coefficient (5.25).
Square it (27.5625) and add it to both sides.

Add '27.5625' to each side of the equation.
10.5x + 27.5625 + x2 = -7.5 + 27.5625

Reorder the terms:
27.5625 + 10.5x + x2 = -7.5 + 27.5625

Combine like terms: -7.5 + 27.5625 = 20.0625
27.5625 + 10.5x + x2 = 20.0625

Factor a perfect square on the left side:
(x + 5.25)(x + 5.25) = 20.0625

Calculate the square root of the right side: 4.479118217

Break this problem into two subproblems by setting 
(x + 5.25) equal to 4.479118217 and -4.479118217.

Subproblem 1

x + 5.25 = 4.479118217 Simplifying x + 5.25 = 4.479118217 Reorder the terms: 5.25 + x = 4.479118217 Solving 5.25 + x = 4.479118217 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5.25' to each side of the equation. 5.25 + -5.25 + x = 4.479118217 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = 4.479118217 + -5.25 x = 4.479118217 + -5.25 Combine like terms: 4.479118217 + -5.25 = -0.770881783 x = -0.770881783 Simplifying x = -0.770881783

Subproblem 2

x + 5.25 = -4.479118217 Simplifying x + 5.25 = -4.479118217 Reorder the terms: 5.25 + x = -4.479118217 Solving 5.25 + x = -4.479118217 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5.25' to each side of the equation. 5.25 + -5.25 + x = -4.479118217 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = -4.479118217 + -5.25 x = -4.479118217 + -5.25 Combine like terms: -4.479118217 + -5.25 = -9.729118217 x = -9.729118217 Simplifying x = -9.729118217

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.770881783, -9.729118217}

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