8x^2-55x-42=0

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Solution for 8x^2-55x-42=0 equation:


Simplifying
8x2 + -55x + -42 = 0

Reorder the terms:
-42 + -55x + 8x2 = 0

Solving
-42 + -55x + 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'.
-5.25 + -6.875x + x2 = 0

Move the constant term to the right:

Add '5.25' to each side of the equation.
-5.25 + -6.875x + 5.25 + x2 = 0 + 5.25

Reorder the terms:
-5.25 + 5.25 + -6.875x + x2 = 0 + 5.25

Combine like terms: -5.25 + 5.25 = 0.00
0.00 + -6.875x + x2 = 0 + 5.25
-6.875x + x2 = 0 + 5.25

Combine like terms: 0 + 5.25 = 5.25
-6.875x + x2 = 5.25

The x term is -6.875x.  Take half its coefficient (-3.4375).
Square it (11.81640625) and add it to both sides.

Add '11.81640625' to each side of the equation.
-6.875x + 11.81640625 + x2 = 5.25 + 11.81640625

Reorder the terms:
11.81640625 + -6.875x + x2 = 5.25 + 11.81640625

Combine like terms: 5.25 + 11.81640625 = 17.06640625
11.81640625 + -6.875x + x2 = 17.06640625

Factor a perfect square on the left side:
(x + -3.4375)(x + -3.4375) = 17.06640625

Calculate the square root of the right side: 4.131150717

Break this problem into two subproblems by setting 
(x + -3.4375) equal to 4.131150717 and -4.131150717.

Subproblem 1

x + -3.4375 = 4.131150717 Simplifying x + -3.4375 = 4.131150717 Reorder the terms: -3.4375 + x = 4.131150717 Solving -3.4375 + x = 4.131150717 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.4375' to each side of the equation. -3.4375 + 3.4375 + x = 4.131150717 + 3.4375 Combine like terms: -3.4375 + 3.4375 = 0.0000 0.0000 + x = 4.131150717 + 3.4375 x = 4.131150717 + 3.4375 Combine like terms: 4.131150717 + 3.4375 = 7.568650717 x = 7.568650717 Simplifying x = 7.568650717

Subproblem 2

x + -3.4375 = -4.131150717 Simplifying x + -3.4375 = -4.131150717 Reorder the terms: -3.4375 + x = -4.131150717 Solving -3.4375 + x = -4.131150717 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.4375' to each side of the equation. -3.4375 + 3.4375 + x = -4.131150717 + 3.4375 Combine like terms: -3.4375 + 3.4375 = 0.0000 0.0000 + x = -4.131150717 + 3.4375 x = -4.131150717 + 3.4375 Combine like terms: -4.131150717 + 3.4375 = -0.693650717 x = -0.693650717 Simplifying x = -0.693650717

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.568650717, -0.693650717}

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