-8x^2+8x+21=0

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Solution for -8x^2+8x+21=0 equation:


Simplifying
-8x2 + 8x + 21 = 0

Reorder the terms:
21 + 8x + -8x2 = 0

Solving
21 + 8x + -8x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
-8 the coefficient of the squared term: 

Divide each side by '-8'.
-2.625 + -1x + x2 = 0

Move the constant term to the right:

Add '2.625' to each side of the equation.
-2.625 + -1x + 2.625 + x2 = 0 + 2.625

Reorder the terms:
-2.625 + 2.625 + -1x + x2 = 0 + 2.625

Combine like terms: -2.625 + 2.625 = 0.000
0.000 + -1x + x2 = 0 + 2.625
-1x + x2 = 0 + 2.625

Combine like terms: 0 + 2.625 = 2.625
-1x + x2 = 2.625

The x term is -1x.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1x + 0.25 + x2 = 2.625 + 0.25

Reorder the terms:
0.25 + -1x + x2 = 2.625 + 0.25

Combine like terms: 2.625 + 0.25 = 2.875
0.25 + -1x + x2 = 2.875

Factor a perfect square on the left side:
(x + -0.5)(x + -0.5) = 2.875

Calculate the square root of the right side: 1.695582496

Break this problem into two subproblems by setting 
(x + -0.5) equal to 1.695582496 and -1.695582496.

Subproblem 1

x + -0.5 = 1.695582496 Simplifying x + -0.5 = 1.695582496 Reorder the terms: -0.5 + x = 1.695582496 Solving -0.5 + x = 1.695582496 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + x = 1.695582496 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + x = 1.695582496 + 0.5 x = 1.695582496 + 0.5 Combine like terms: 1.695582496 + 0.5 = 2.195582496 x = 2.195582496 Simplifying x = 2.195582496

Subproblem 2

x + -0.5 = -1.695582496 Simplifying x + -0.5 = -1.695582496 Reorder the terms: -0.5 + x = -1.695582496 Solving -0.5 + x = -1.695582496 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + x = -1.695582496 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + x = -1.695582496 + 0.5 x = -1.695582496 + 0.5 Combine like terms: -1.695582496 + 0.5 = -1.195582496 x = -1.195582496 Simplifying x = -1.195582496

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.195582496, -1.195582496}

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