21x^2+116x+80=0

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Solution for 21x^2+116x+80=0 equation:


Simplifying
21x2 + 116x + 80 = 0

Reorder the terms:
80 + 116x + 21x2 = 0

Solving
80 + 116x + 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'.
3.80952381 + 5.523809524x + x2 = 0

Move the constant term to the right:

Add '-3.80952381' to each side of the equation.
3.80952381 + 5.523809524x + -3.80952381 + x2 = 0 + -3.80952381

Reorder the terms:
3.80952381 + -3.80952381 + 5.523809524x + x2 = 0 + -3.80952381

Combine like terms: 3.80952381 + -3.80952381 = 0.00000000
0.00000000 + 5.523809524x + x2 = 0 + -3.80952381
5.523809524x + x2 = 0 + -3.80952381

Combine like terms: 0 + -3.80952381 = -3.80952381
5.523809524x + x2 = -3.80952381

The x term is 5.523809524x.  Take half its coefficient (2.761904762).
Square it (7.628117914) and add it to both sides.

Add '7.628117914' to each side of the equation.
5.523809524x + 7.628117914 + x2 = -3.80952381 + 7.628117914

Reorder the terms:
7.628117914 + 5.523809524x + x2 = -3.80952381 + 7.628117914

Combine like terms: -3.80952381 + 7.628117914 = 3.818594104
7.628117914 + 5.523809524x + x2 = 3.818594104

Factor a perfect square on the left side:
(x + 2.761904762)(x + 2.761904762) = 3.818594104

Calculate the square root of the right side: 1.954122336

Break this problem into two subproblems by setting 
(x + 2.761904762) equal to 1.954122336 and -1.954122336.

Subproblem 1

x + 2.761904762 = 1.954122336 Simplifying x + 2.761904762 = 1.954122336 Reorder the terms: 2.761904762 + x = 1.954122336 Solving 2.761904762 + x = 1.954122336 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.761904762' to each side of the equation. 2.761904762 + -2.761904762 + x = 1.954122336 + -2.761904762 Combine like terms: 2.761904762 + -2.761904762 = 0.000000000 0.000000000 + x = 1.954122336 + -2.761904762 x = 1.954122336 + -2.761904762 Combine like terms: 1.954122336 + -2.761904762 = -0.807782426 x = -0.807782426 Simplifying x = -0.807782426

Subproblem 2

x + 2.761904762 = -1.954122336 Simplifying x + 2.761904762 = -1.954122336 Reorder the terms: 2.761904762 + x = -1.954122336 Solving 2.761904762 + x = -1.954122336 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.761904762' to each side of the equation. 2.761904762 + -2.761904762 + x = -1.954122336 + -2.761904762 Combine like terms: 2.761904762 + -2.761904762 = 0.000000000 0.000000000 + x = -1.954122336 + -2.761904762 x = -1.954122336 + -2.761904762 Combine like terms: -1.954122336 + -2.761904762 = -4.716027098 x = -4.716027098 Simplifying x = -4.716027098

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.807782426, -4.716027098}

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