5x^2-x-8=0

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Solution for 5x^2-x-8=0 equation:


Simplifying
5x2 + -1x + -8 = 0

Reorder the terms:
-8 + -1x + 5x2 = 0

Solving
-8 + -1x + 5x2 = 0

Solving for variable 'x'.

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

Divide each side by '5'.
-1.6 + -0.2x + x2 = 0

Move the constant term to the right:

Add '1.6' to each side of the equation.
-1.6 + -0.2x + 1.6 + x2 = 0 + 1.6

Reorder the terms:
-1.6 + 1.6 + -0.2x + x2 = 0 + 1.6

Combine like terms: -1.6 + 1.6 = 0.0
0.0 + -0.2x + x2 = 0 + 1.6
-0.2x + x2 = 0 + 1.6

Combine like terms: 0 + 1.6 = 1.6
-0.2x + x2 = 1.6

The x term is -0.2x.  Take half its coefficient (-0.1).
Square it (0.01) and add it to both sides.

Add '0.01' to each side of the equation.
-0.2x + 0.01 + x2 = 1.6 + 0.01

Reorder the terms:
0.01 + -0.2x + x2 = 1.6 + 0.01

Combine like terms: 1.6 + 0.01 = 1.61
0.01 + -0.2x + x2 = 1.61

Factor a perfect square on the left side:
(x + -0.1)(x + -0.1) = 1.61

Calculate the square root of the right side: 1.268857754

Break this problem into two subproblems by setting 
(x + -0.1) equal to 1.268857754 and -1.268857754.

Subproblem 1

x + -0.1 = 1.268857754 Simplifying x + -0.1 = 1.268857754 Reorder the terms: -0.1 + x = 1.268857754 Solving -0.1 + x = 1.268857754 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.1' to each side of the equation. -0.1 + 0.1 + x = 1.268857754 + 0.1 Combine like terms: -0.1 + 0.1 = 0.0 0.0 + x = 1.268857754 + 0.1 x = 1.268857754 + 0.1 Combine like terms: 1.268857754 + 0.1 = 1.368857754 x = 1.368857754 Simplifying x = 1.368857754

Subproblem 2

x + -0.1 = -1.268857754 Simplifying x + -0.1 = -1.268857754 Reorder the terms: -0.1 + x = -1.268857754 Solving -0.1 + x = -1.268857754 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.1' to each side of the equation. -0.1 + 0.1 + x = -1.268857754 + 0.1 Combine like terms: -0.1 + 0.1 = 0.0 0.0 + x = -1.268857754 + 0.1 x = -1.268857754 + 0.1 Combine like terms: -1.268857754 + 0.1 = -1.168857754 x = -1.168857754 Simplifying x = -1.168857754

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.368857754, -1.168857754}

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