8x^2+21=39x

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Solution for 8x^2+21=39x equation:


Simplifying
8x2 + 21 = 39x

Reorder the terms:
21 + 8x2 = 39x

Solving
21 + 8x2 = 39x

Solving for variable 'x'.

Reorder the terms:
21 + -39x + 8x2 = 39x + -39x

Combine like terms: 39x + -39x = 0
21 + -39x + 8x2 = 0

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

Divide each side by '8'.
2.625 + -4.875x + x2 = 0

Move the constant term to the right:

Add '-2.625' to each side of the equation.
2.625 + -4.875x + -2.625 + x2 = 0 + -2.625

Reorder the terms:
2.625 + -2.625 + -4.875x + x2 = 0 + -2.625

Combine like terms: 2.625 + -2.625 = 0.000
0.000 + -4.875x + x2 = 0 + -2.625
-4.875x + x2 = 0 + -2.625

Combine like terms: 0 + -2.625 = -2.625
-4.875x + x2 = -2.625

The x term is -4.875x.  Take half its coefficient (-2.4375).
Square it (5.94140625) and add it to both sides.

Add '5.94140625' to each side of the equation.
-4.875x + 5.94140625 + x2 = -2.625 + 5.94140625

Reorder the terms:
5.94140625 + -4.875x + x2 = -2.625 + 5.94140625

Combine like terms: -2.625 + 5.94140625 = 3.31640625
5.94140625 + -4.875x + x2 = 3.31640625

Factor a perfect square on the left side:
(x + -2.4375)(x + -2.4375) = 3.31640625

Calculate the square root of the right side: 1.821100286

Break this problem into two subproblems by setting 
(x + -2.4375) equal to 1.821100286 and -1.821100286.

Subproblem 1

x + -2.4375 = 1.821100286 Simplifying x + -2.4375 = 1.821100286 Reorder the terms: -2.4375 + x = 1.821100286 Solving -2.4375 + x = 1.821100286 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.4375' to each side of the equation. -2.4375 + 2.4375 + x = 1.821100286 + 2.4375 Combine like terms: -2.4375 + 2.4375 = 0.0000 0.0000 + x = 1.821100286 + 2.4375 x = 1.821100286 + 2.4375 Combine like terms: 1.821100286 + 2.4375 = 4.258600286 x = 4.258600286 Simplifying x = 4.258600286

Subproblem 2

x + -2.4375 = -1.821100286 Simplifying x + -2.4375 = -1.821100286 Reorder the terms: -2.4375 + x = -1.821100286 Solving -2.4375 + x = -1.821100286 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.4375' to each side of the equation. -2.4375 + 2.4375 + x = -1.821100286 + 2.4375 Combine like terms: -2.4375 + 2.4375 = 0.0000 0.0000 + x = -1.821100286 + 2.4375 x = -1.821100286 + 2.4375 Combine like terms: -1.821100286 + 2.4375 = 0.616399714 x = 0.616399714 Simplifying x = 0.616399714

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.258600286, 0.616399714}

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