21x^2+120x+104=0

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Solution for 21x^2+120x+104=0 equation:


Simplifying
21x2 + 120x + 104 = 0

Reorder the terms:
104 + 120x + 21x2 = 0

Solving
104 + 120x + 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'.
4.952380952 + 5.714285714x + x2 = 0

Move the constant term to the right:

Add '-4.952380952' to each side of the equation.
4.952380952 + 5.714285714x + -4.952380952 + x2 = 0 + -4.952380952

Reorder the terms:
4.952380952 + -4.952380952 + 5.714285714x + x2 = 0 + -4.952380952

Combine like terms: 4.952380952 + -4.952380952 = 0.000000000
0.000000000 + 5.714285714x + x2 = 0 + -4.952380952
5.714285714x + x2 = 0 + -4.952380952

Combine like terms: 0 + -4.952380952 = -4.952380952
5.714285714x + x2 = -4.952380952

The x term is 5.714285714x.  Take half its coefficient (2.857142857).
Square it (8.163265305) and add it to both sides.

Add '8.163265305' to each side of the equation.
5.714285714x + 8.163265305 + x2 = -4.952380952 + 8.163265305

Reorder the terms:
8.163265305 + 5.714285714x + x2 = -4.952380952 + 8.163265305

Combine like terms: -4.952380952 + 8.163265305 = 3.210884353
8.163265305 + 5.714285714x + x2 = 3.210884353

Factor a perfect square on the left side:
(x + 2.857142857)(x + 2.857142857) = 3.210884353

Calculate the square root of the right side: 1.791894069

Break this problem into two subproblems by setting 
(x + 2.857142857) equal to 1.791894069 and -1.791894069.

Subproblem 1

x + 2.857142857 = 1.791894069 Simplifying x + 2.857142857 = 1.791894069 Reorder the terms: 2.857142857 + x = 1.791894069 Solving 2.857142857 + x = 1.791894069 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.857142857' to each side of the equation. 2.857142857 + -2.857142857 + x = 1.791894069 + -2.857142857 Combine like terms: 2.857142857 + -2.857142857 = 0.000000000 0.000000000 + x = 1.791894069 + -2.857142857 x = 1.791894069 + -2.857142857 Combine like terms: 1.791894069 + -2.857142857 = -1.065248788 x = -1.065248788 Simplifying x = -1.065248788

Subproblem 2

x + 2.857142857 = -1.791894069 Simplifying x + 2.857142857 = -1.791894069 Reorder the terms: 2.857142857 + x = -1.791894069 Solving 2.857142857 + x = -1.791894069 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.857142857' to each side of the equation. 2.857142857 + -2.857142857 + x = -1.791894069 + -2.857142857 Combine like terms: 2.857142857 + -2.857142857 = 0.000000000 0.000000000 + x = -1.791894069 + -2.857142857 x = -1.791894069 + -2.857142857 Combine like terms: -1.791894069 + -2.857142857 = -4.649036926 x = -4.649036926 Simplifying x = -4.649036926

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-1.065248788, -4.649036926}

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