-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 = 35.0625
27.5625 + -10.5x + x2 = 35.0625

Factor a perfect square on the left side:
(x + -5.25)(x + -5.25) = 35.0625

Calculate the square root of the right side: 5.921359641

Break this problem into two subproblems by setting 
(x + -5.25) equal to 5.921359641 and -5.921359641.

Subproblem 1

x + -5.25 = 5.921359641 Simplifying x + -5.25 = 5.921359641 Reorder the terms: -5.25 + x = 5.921359641 Solving -5.25 + x = 5.921359641 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 = 5.921359641 + 5.25 Combine like terms: -5.25 + 5.25 = 0.00 0.00 + x = 5.921359641 + 5.25 x = 5.921359641 + 5.25 Combine like terms: 5.921359641 + 5.25 = 11.171359641 x = 11.171359641 Simplifying x = 11.171359641

Subproblem 2

x + -5.25 = -5.921359641 Simplifying x + -5.25 = -5.921359641 Reorder the terms: -5.25 + x = -5.921359641 Solving -5.25 + x = -5.921359641 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 = -5.921359641 + 5.25 Combine like terms: -5.25 + 5.25 = 0.00 0.00 + x = -5.921359641 + 5.25 x = -5.921359641 + 5.25 Combine like terms: -5.921359641 + 5.25 = -0.671359641 x = -0.671359641 Simplifying x = -0.671359641

Solution

The solution to the problem is based on the solutions from the subproblems. x = {11.171359641, -0.671359641}

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