21x^2-40x-128=0

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Solution for 21x^2-40x-128=0 equation:


Simplifying
21x2 + -40x + -128 = 0

Reorder the terms:
-128 + -40x + 21x2 = 0

Solving
-128 + -40x + 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'.
-6.095238095 + -1.904761905x + x2 = 0

Move the constant term to the right:

Add '6.095238095' to each side of the equation.
-6.095238095 + -1.904761905x + 6.095238095 + x2 = 0 + 6.095238095

Reorder the terms:
-6.095238095 + 6.095238095 + -1.904761905x + x2 = 0 + 6.095238095

Combine like terms: -6.095238095 + 6.095238095 = 0.000000000
0.000000000 + -1.904761905x + x2 = 0 + 6.095238095
-1.904761905x + x2 = 0 + 6.095238095

Combine like terms: 0 + 6.095238095 = 6.095238095
-1.904761905x + x2 = 6.095238095

The x term is -1.904761905x.  Take half its coefficient (-0.9523809525).
Square it (0.9070294787) and add it to both sides.

Add '0.9070294787' to each side of the equation.
-1.904761905x + 0.9070294787 + x2 = 6.095238095 + 0.9070294787

Reorder the terms:
0.9070294787 + -1.904761905x + x2 = 6.095238095 + 0.9070294787

Combine like terms: 6.095238095 + 0.9070294787 = 7.0022675737
0.9070294787 + -1.904761905x + x2 = 7.0022675737

Factor a perfect square on the left side:
(x + -0.9523809525)(x + -0.9523809525) = 7.0022675737

Calculate the square root of the right side: 2.646179808

Break this problem into two subproblems by setting 
(x + -0.9523809525) equal to 2.646179808 and -2.646179808.

Subproblem 1

x + -0.9523809525 = 2.646179808 Simplifying x + -0.9523809525 = 2.646179808 Reorder the terms: -0.9523809525 + x = 2.646179808 Solving -0.9523809525 + x = 2.646179808 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.9523809525' to each side of the equation. -0.9523809525 + 0.9523809525 + x = 2.646179808 + 0.9523809525 Combine like terms: -0.9523809525 + 0.9523809525 = 0.0000000000 0.0000000000 + x = 2.646179808 + 0.9523809525 x = 2.646179808 + 0.9523809525 Combine like terms: 2.646179808 + 0.9523809525 = 3.5985607605 x = 3.5985607605 Simplifying x = 3.5985607605

Subproblem 2

x + -0.9523809525 = -2.646179808 Simplifying x + -0.9523809525 = -2.646179808 Reorder the terms: -0.9523809525 + x = -2.646179808 Solving -0.9523809525 + x = -2.646179808 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.9523809525' to each side of the equation. -0.9523809525 + 0.9523809525 + x = -2.646179808 + 0.9523809525 Combine like terms: -0.9523809525 + 0.9523809525 = 0.0000000000 0.0000000000 + x = -2.646179808 + 0.9523809525 x = -2.646179808 + 0.9523809525 Combine like terms: -2.646179808 + 0.9523809525 = -1.6937988555 x = -1.6937988555 Simplifying x = -1.6937988555

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.5985607605, -1.6937988555}

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