21x^2-47x-120=0

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Solution for 21x^2-47x-120=0 equation:


Simplifying
21x2 + -47x + -120 = 0

Reorder the terms:
-120 + -47x + 21x2 = 0

Solving
-120 + -47x + 21x2 = 0

Solving for variable 'x'.

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

Divide each side by '21'.
-5.714285714 + -2.238095238x + x2 = 0

Move the constant term to the right:

Add '5.714285714' to each side of the equation.
-5.714285714 + -2.238095238x + 5.714285714 + x2 = 0 + 5.714285714

Reorder the terms:
-5.714285714 + 5.714285714 + -2.238095238x + x2 = 0 + 5.714285714

Combine like terms: -5.714285714 + 5.714285714 = 0.000000000
0.000000000 + -2.238095238x + x2 = 0 + 5.714285714
-2.238095238x + x2 = 0 + 5.714285714

Combine like terms: 0 + 5.714285714 = 5.714285714
-2.238095238x + x2 = 5.714285714

The x term is -2.238095238x.  Take half its coefficient (-1.119047619).
Square it (1.252267574) and add it to both sides.

Add '1.252267574' to each side of the equation.
-2.238095238x + 1.252267574 + x2 = 5.714285714 + 1.252267574

Reorder the terms:
1.252267574 + -2.238095238x + x2 = 5.714285714 + 1.252267574

Combine like terms: 5.714285714 + 1.252267574 = 6.966553288
1.252267574 + -2.238095238x + x2 = 6.966553288

Factor a perfect square on the left side:
(x + -1.119047619)(x + -1.119047619) = 6.966553288

Calculate the square root of the right side: 2.639422908

Break this problem into two subproblems by setting 
(x + -1.119047619) equal to 2.639422908 and -2.639422908.

Subproblem 1

x + -1.119047619 = 2.639422908 Simplifying x + -1.119047619 = 2.639422908 Reorder the terms: -1.119047619 + x = 2.639422908 Solving -1.119047619 + x = 2.639422908 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.119047619' to each side of the equation. -1.119047619 + 1.119047619 + x = 2.639422908 + 1.119047619 Combine like terms: -1.119047619 + 1.119047619 = 0.000000000 0.000000000 + x = 2.639422908 + 1.119047619 x = 2.639422908 + 1.119047619 Combine like terms: 2.639422908 + 1.119047619 = 3.758470527 x = 3.758470527 Simplifying x = 3.758470527

Subproblem 2

x + -1.119047619 = -2.639422908 Simplifying x + -1.119047619 = -2.639422908 Reorder the terms: -1.119047619 + x = -2.639422908 Solving -1.119047619 + x = -2.639422908 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.119047619' to each side of the equation. -1.119047619 + 1.119047619 + x = -2.639422908 + 1.119047619 Combine like terms: -1.119047619 + 1.119047619 = 0.000000000 0.000000000 + x = -2.639422908 + 1.119047619 x = -2.639422908 + 1.119047619 Combine like terms: -2.639422908 + 1.119047619 = -1.520375289 x = -1.520375289 Simplifying x = -1.520375289

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.758470527, -1.520375289}

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