8x^2+8x=21

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


Simplifying
8x2 + 8x = 21

Reorder the terms:
8x + 8x2 = 21

Solving
8x + 8x2 = 21

Solving for variable 'x'.

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

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

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

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

Move the constant term to the right:

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

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

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

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

The x term is x.  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.
 + 0.25 + x2 = 2.625 + 0.25

Combine like terms:  + 0.25 = 1.25
1.25 + x2 = 2.625 + 0.25

Combine like terms: 2.625 + 0.25 = 2.875
1.25 + 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 = 1.195582496 x = 1.195582496 Simplifying x = 1.195582496

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 = -2.195582496 x = -2.195582496 Simplifying x = -2.195582496

Solution

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

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