8x^2-13x-20=0

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Solution for 8x^2-13x-20=0 equation:


Simplifying
8x2 + -13x + -20 = 0

Reorder the terms:
-20 + -13x + 8x2 = 0

Solving
-20 + -13x + 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'.
-2.5 + -1.625x + x2 = 0

Move the constant term to the right:

Add '2.5' to each side of the equation.
-2.5 + -1.625x + 2.5 + x2 = 0 + 2.5

Reorder the terms:
-2.5 + 2.5 + -1.625x + x2 = 0 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + -1.625x + x2 = 0 + 2.5
-1.625x + x2 = 0 + 2.5

Combine like terms: 0 + 2.5 = 2.5
-1.625x + x2 = 2.5

The x term is -1.625x.  Take half its coefficient (-0.8125).
Square it (0.66015625) and add it to both sides.

Add '0.66015625' to each side of the equation.
-1.625x + 0.66015625 + x2 = 2.5 + 0.66015625

Reorder the terms:
0.66015625 + -1.625x + x2 = 2.5 + 0.66015625

Combine like terms: 2.5 + 0.66015625 = 3.16015625
0.66015625 + -1.625x + x2 = 3.16015625

Factor a perfect square on the left side:
(x + -0.8125)(x + -0.8125) = 3.16015625

Calculate the square root of the right side: 1.777682832

Break this problem into two subproblems by setting 
(x + -0.8125) equal to 1.777682832 and -1.777682832.

Subproblem 1

x + -0.8125 = 1.777682832 Simplifying x + -0.8125 = 1.777682832 Reorder the terms: -0.8125 + x = 1.777682832 Solving -0.8125 + x = 1.777682832 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.8125' to each side of the equation. -0.8125 + 0.8125 + x = 1.777682832 + 0.8125 Combine like terms: -0.8125 + 0.8125 = 0.0000 0.0000 + x = 1.777682832 + 0.8125 x = 1.777682832 + 0.8125 Combine like terms: 1.777682832 + 0.8125 = 2.590182832 x = 2.590182832 Simplifying x = 2.590182832

Subproblem 2

x + -0.8125 = -1.777682832 Simplifying x + -0.8125 = -1.777682832 Reorder the terms: -0.8125 + x = -1.777682832 Solving -0.8125 + x = -1.777682832 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.8125' to each side of the equation. -0.8125 + 0.8125 + x = -1.777682832 + 0.8125 Combine like terms: -0.8125 + 0.8125 = 0.0000 0.0000 + x = -1.777682832 + 0.8125 x = -1.777682832 + 0.8125 Combine like terms: -1.777682832 + 0.8125 = -0.965182832 x = -0.965182832 Simplifying x = -0.965182832

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.590182832, -0.965182832}

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