21x^2-28x=8

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Solution for 21x^2-28x=8 equation:


Simplifying
21x2 + -28x = 8

Reorder the terms:
-28x + 21x2 = 8

Solving
-28x + 21x2 = 8

Solving for variable 'x'.

Reorder the terms:
-8 + -28x + 21x2 = 8 + -8

Combine like terms: 8 + -8 = 0
-8 + -28x + 21x2 = 0

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

Divide each side by '21'.
-0.380952381 + -1.333333333x + x2 = 0

Move the constant term to the right:

Add '0.380952381' to each side of the equation.
-0.380952381 + -1.333333333x + 0.380952381 + x2 = 0 + 0.380952381

Reorder the terms:
-0.380952381 + 0.380952381 + -1.333333333x + x2 = 0 + 0.380952381

Combine like terms: -0.380952381 + 0.380952381 = 0.000000000
0.000000000 + -1.333333333x + x2 = 0 + 0.380952381
-1.333333333x + x2 = 0 + 0.380952381

Combine like terms: 0 + 0.380952381 = 0.380952381
-1.333333333x + x2 = 0.380952381

The x term is -1.333333333x.  Take half its coefficient (-0.6666666665).
Square it (0.4444444442) and add it to both sides.

Add '0.4444444442' to each side of the equation.
-1.333333333x + 0.4444444442 + x2 = 0.380952381 + 0.4444444442

Reorder the terms:
0.4444444442 + -1.333333333x + x2 = 0.380952381 + 0.4444444442

Combine like terms: 0.380952381 + 0.4444444442 = 0.8253968252
0.4444444442 + -1.333333333x + x2 = 0.8253968252

Factor a perfect square on the left side:
(x + -0.6666666665)(x + -0.6666666665) = 0.8253968252

Calculate the square root of the right side: 0.908513525

Break this problem into two subproblems by setting 
(x + -0.6666666665) equal to 0.908513525 and -0.908513525.

Subproblem 1

x + -0.6666666665 = 0.908513525 Simplifying x + -0.6666666665 = 0.908513525 Reorder the terms: -0.6666666665 + x = 0.908513525 Solving -0.6666666665 + x = 0.908513525 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.6666666665' to each side of the equation. -0.6666666665 + 0.6666666665 + x = 0.908513525 + 0.6666666665 Combine like terms: -0.6666666665 + 0.6666666665 = 0.0000000000 0.0000000000 + x = 0.908513525 + 0.6666666665 x = 0.908513525 + 0.6666666665 Combine like terms: 0.908513525 + 0.6666666665 = 1.5751801915 x = 1.5751801915 Simplifying x = 1.5751801915

Subproblem 2

x + -0.6666666665 = -0.908513525 Simplifying x + -0.6666666665 = -0.908513525 Reorder the terms: -0.6666666665 + x = -0.908513525 Solving -0.6666666665 + x = -0.908513525 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.6666666665' to each side of the equation. -0.6666666665 + 0.6666666665 + x = -0.908513525 + 0.6666666665 Combine like terms: -0.6666666665 + 0.6666666665 = 0.0000000000 0.0000000000 + x = -0.908513525 + 0.6666666665 x = -0.908513525 + 0.6666666665 Combine like terms: -0.908513525 + 0.6666666665 = -0.2418468585 x = -0.2418468585 Simplifying x = -0.2418468585

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.5751801915, -0.2418468585}

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