8x^2-7x-20=0

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Solution for 8x^2-7x-20=0 equation:


Simplifying
8x2 + -7x + -20 = 0

Reorder the terms:
-20 + -7x + 8x2 = 0

Solving
-20 + -7x + 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 + -0.875x + x2 = 0

Move the constant term to the right:

Add '2.5' to each side of the equation.
-2.5 + -0.875x + 2.5 + x2 = 0 + 2.5

Reorder the terms:
-2.5 + 2.5 + -0.875x + x2 = 0 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + -0.875x + x2 = 0 + 2.5
-0.875x + x2 = 0 + 2.5

Combine like terms: 0 + 2.5 = 2.5
-0.875x + x2 = 2.5

The x term is -0.875x.  Take half its coefficient (-0.4375).
Square it (0.19140625) and add it to both sides.

Add '0.19140625' to each side of the equation.
-0.875x + 0.19140625 + x2 = 2.5 + 0.19140625

Reorder the terms:
0.19140625 + -0.875x + x2 = 2.5 + 0.19140625

Combine like terms: 2.5 + 0.19140625 = 2.69140625
0.19140625 + -0.875x + x2 = 2.69140625

Factor a perfect square on the left side:
(x + -0.4375)(x + -0.4375) = 2.69140625

Calculate the square root of the right side: 1.640550594

Break this problem into two subproblems by setting 
(x + -0.4375) equal to 1.640550594 and -1.640550594.

Subproblem 1

x + -0.4375 = 1.640550594 Simplifying x + -0.4375 = 1.640550594 Reorder the terms: -0.4375 + x = 1.640550594 Solving -0.4375 + x = 1.640550594 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.4375' to each side of the equation. -0.4375 + 0.4375 + x = 1.640550594 + 0.4375 Combine like terms: -0.4375 + 0.4375 = 0.0000 0.0000 + x = 1.640550594 + 0.4375 x = 1.640550594 + 0.4375 Combine like terms: 1.640550594 + 0.4375 = 2.078050594 x = 2.078050594 Simplifying x = 2.078050594

Subproblem 2

x + -0.4375 = -1.640550594 Simplifying x + -0.4375 = -1.640550594 Reorder the terms: -0.4375 + x = -1.640550594 Solving -0.4375 + x = -1.640550594 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.4375' to each side of the equation. -0.4375 + 0.4375 + x = -1.640550594 + 0.4375 Combine like terms: -0.4375 + 0.4375 = 0.0000 0.0000 + x = -1.640550594 + 0.4375 x = -1.640550594 + 0.4375 Combine like terms: -1.640550594 + 0.4375 = -1.203050594 x = -1.203050594 Simplifying x = -1.203050594

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.078050594, -1.203050594}

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