8x^2-43x-21=0

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Solution for 8x^2-43x-21=0 equation:


Simplifying
8x2 + -43x + -21 = 0

Reorder the terms:
-21 + -43x + 8x2 = 0

Solving
-21 + -43x + 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 + -5.375x + x2 = 0

Move the constant term to the right:

Add '2.625' to each side of the equation.
-2.625 + -5.375x + 2.625 + x2 = 0 + 2.625

Reorder the terms:
-2.625 + 2.625 + -5.375x + x2 = 0 + 2.625

Combine like terms: -2.625 + 2.625 = 0.000
0.000 + -5.375x + x2 = 0 + 2.625
-5.375x + x2 = 0 + 2.625

Combine like terms: 0 + 2.625 = 2.625
-5.375x + x2 = 2.625

The x term is -5.375x.  Take half its coefficient (-2.6875).
Square it (7.22265625) and add it to both sides.

Add '7.22265625' to each side of the equation.
-5.375x + 7.22265625 + x2 = 2.625 + 7.22265625

Reorder the terms:
7.22265625 + -5.375x + x2 = 2.625 + 7.22265625

Combine like terms: 2.625 + 7.22265625 = 9.84765625
7.22265625 + -5.375x + x2 = 9.84765625

Factor a perfect square on the left side:
(x + -2.6875)(x + -2.6875) = 9.84765625

Calculate the square root of the right side: 3.138097553

Break this problem into two subproblems by setting 
(x + -2.6875) equal to 3.138097553 and -3.138097553.

Subproblem 1

x + -2.6875 = 3.138097553 Simplifying x + -2.6875 = 3.138097553 Reorder the terms: -2.6875 + x = 3.138097553 Solving -2.6875 + x = 3.138097553 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.6875' to each side of the equation. -2.6875 + 2.6875 + x = 3.138097553 + 2.6875 Combine like terms: -2.6875 + 2.6875 = 0.0000 0.0000 + x = 3.138097553 + 2.6875 x = 3.138097553 + 2.6875 Combine like terms: 3.138097553 + 2.6875 = 5.825597553 x = 5.825597553 Simplifying x = 5.825597553

Subproblem 2

x + -2.6875 = -3.138097553 Simplifying x + -2.6875 = -3.138097553 Reorder the terms: -2.6875 + x = -3.138097553 Solving -2.6875 + x = -3.138097553 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.6875' to each side of the equation. -2.6875 + 2.6875 + x = -3.138097553 + 2.6875 Combine like terms: -2.6875 + 2.6875 = 0.0000 0.0000 + x = -3.138097553 + 2.6875 x = -3.138097553 + 2.6875 Combine like terms: -3.138097553 + 2.6875 = -0.450597553 x = -0.450597553 Simplifying x = -0.450597553

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.825597553, -0.450597553}

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