2x^2+21x-258=0

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Solution for 2x^2+21x-258=0 equation:


Simplifying
2x2 + 21x + -258 = 0

Reorder the terms:
-258 + 21x + 2x2 = 0

Solving
-258 + 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'.
-129 + 10.5x + x2 = 0

Move the constant term to the right:

Add '129' to each side of the equation.
-129 + 10.5x + 129 + x2 = 0 + 129

Reorder the terms:
-129 + 129 + 10.5x + x2 = 0 + 129

Combine like terms: -129 + 129 = 0
0 + 10.5x + x2 = 0 + 129
10.5x + x2 = 0 + 129

Combine like terms: 0 + 129 = 129
10.5x + x2 = 129

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 = 129 + 27.5625

Reorder the terms:
27.5625 + 10.5x + x2 = 129 + 27.5625

Combine like terms: 129 + 27.5625 = 156.5625
27.5625 + 10.5x + x2 = 156.5625

Factor a perfect square on the left side:
(x + 5.25)(x + 5.25) = 156.5625

Calculate the square root of the right side: 12.512493756

Break this problem into two subproblems by setting 
(x + 5.25) equal to 12.512493756 and -12.512493756.

Subproblem 1

x + 5.25 = 12.512493756 Simplifying x + 5.25 = 12.512493756 Reorder the terms: 5.25 + x = 12.512493756 Solving 5.25 + x = 12.512493756 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 = 12.512493756 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = 12.512493756 + -5.25 x = 12.512493756 + -5.25 Combine like terms: 12.512493756 + -5.25 = 7.262493756 x = 7.262493756 Simplifying x = 7.262493756

Subproblem 2

x + 5.25 = -12.512493756 Simplifying x + 5.25 = -12.512493756 Reorder the terms: 5.25 + x = -12.512493756 Solving 5.25 + x = -12.512493756 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 = -12.512493756 + -5.25 Combine like terms: 5.25 + -5.25 = 0.00 0.00 + x = -12.512493756 + -5.25 x = -12.512493756 + -5.25 Combine like terms: -12.512493756 + -5.25 = -17.762493756 x = -17.762493756 Simplifying x = -17.762493756

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.262493756, -17.762493756}

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