8x^2-20x-9=0

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Solution for 8x^2-20x-9=0 equation:


Simplifying
8x2 + -20x + -9 = 0

Reorder the terms:
-9 + -20x + 8x2 = 0

Solving
-9 + -20x + 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'.
-1.125 + -2.5x + x2 = 0

Move the constant term to the right:

Add '1.125' to each side of the equation.
-1.125 + -2.5x + 1.125 + x2 = 0 + 1.125

Reorder the terms:
-1.125 + 1.125 + -2.5x + x2 = 0 + 1.125

Combine like terms: -1.125 + 1.125 = 0.000
0.000 + -2.5x + x2 = 0 + 1.125
-2.5x + x2 = 0 + 1.125

Combine like terms: 0 + 1.125 = 1.125
-2.5x + x2 = 1.125

The x term is -2.5x.  Take half its coefficient (-1.25).
Square it (1.5625) and add it to both sides.

Add '1.5625' to each side of the equation.
-2.5x + 1.5625 + x2 = 1.125 + 1.5625

Reorder the terms:
1.5625 + -2.5x + x2 = 1.125 + 1.5625

Combine like terms: 1.125 + 1.5625 = 2.6875
1.5625 + -2.5x + x2 = 2.6875

Factor a perfect square on the left side:
(x + -1.25)(x + -1.25) = 2.6875

Calculate the square root of the right side: 1.639359631

Break this problem into two subproblems by setting 
(x + -1.25) equal to 1.639359631 and -1.639359631.

Subproblem 1

x + -1.25 = 1.639359631 Simplifying x + -1.25 = 1.639359631 Reorder the terms: -1.25 + x = 1.639359631 Solving -1.25 + x = 1.639359631 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.25' to each side of the equation. -1.25 + 1.25 + x = 1.639359631 + 1.25 Combine like terms: -1.25 + 1.25 = 0.00 0.00 + x = 1.639359631 + 1.25 x = 1.639359631 + 1.25 Combine like terms: 1.639359631 + 1.25 = 2.889359631 x = 2.889359631 Simplifying x = 2.889359631

Subproblem 2

x + -1.25 = -1.639359631 Simplifying x + -1.25 = -1.639359631 Reorder the terms: -1.25 + x = -1.639359631 Solving -1.25 + x = -1.639359631 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.25' to each side of the equation. -1.25 + 1.25 + x = -1.639359631 + 1.25 Combine like terms: -1.25 + 1.25 = 0.00 0.00 + x = -1.639359631 + 1.25 x = -1.639359631 + 1.25 Combine like terms: -1.639359631 + 1.25 = -0.389359631 x = -0.389359631 Simplifying x = -0.389359631

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.889359631, -0.389359631}

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