4x^2-5x-81=0

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Solution for 4x^2-5x-81=0 equation:


Simplifying
4x2 + -5x + -81 = 0

Reorder the terms:
-81 + -5x + 4x2 = 0

Solving
-81 + -5x + 4x2 = 0

Solving for variable 'x'.

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

Divide each side by '4'.
-20.25 + -1.25x + x2 = 0

Move the constant term to the right:

Add '20.25' to each side of the equation.
-20.25 + -1.25x + 20.25 + x2 = 0 + 20.25

Reorder the terms:
-20.25 + 20.25 + -1.25x + x2 = 0 + 20.25

Combine like terms: -20.25 + 20.25 = 0.00
0.00 + -1.25x + x2 = 0 + 20.25
-1.25x + x2 = 0 + 20.25

Combine like terms: 0 + 20.25 = 20.25
-1.25x + x2 = 20.25

The x term is -1.25x.  Take half its coefficient (-0.625).
Square it (0.390625) and add it to both sides.

Add '0.390625' to each side of the equation.
-1.25x + 0.390625 + x2 = 20.25 + 0.390625

Reorder the terms:
0.390625 + -1.25x + x2 = 20.25 + 0.390625

Combine like terms: 20.25 + 0.390625 = 20.640625
0.390625 + -1.25x + x2 = 20.640625

Factor a perfect square on the left side:
(x + -0.625)(x + -0.625) = 20.640625

Calculate the square root of the right side: 4.543195461

Break this problem into two subproblems by setting 
(x + -0.625) equal to 4.543195461 and -4.543195461.

Subproblem 1

x + -0.625 = 4.543195461 Simplifying x + -0.625 = 4.543195461 Reorder the terms: -0.625 + x = 4.543195461 Solving -0.625 + x = 4.543195461 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.625' to each side of the equation. -0.625 + 0.625 + x = 4.543195461 + 0.625 Combine like terms: -0.625 + 0.625 = 0.000 0.000 + x = 4.543195461 + 0.625 x = 4.543195461 + 0.625 Combine like terms: 4.543195461 + 0.625 = 5.168195461 x = 5.168195461 Simplifying x = 5.168195461

Subproblem 2

x + -0.625 = -4.543195461 Simplifying x + -0.625 = -4.543195461 Reorder the terms: -0.625 + x = -4.543195461 Solving -0.625 + x = -4.543195461 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.625' to each side of the equation. -0.625 + 0.625 + x = -4.543195461 + 0.625 Combine like terms: -0.625 + 0.625 = 0.000 0.000 + x = -4.543195461 + 0.625 x = -4.543195461 + 0.625 Combine like terms: -4.543195461 + 0.625 = -3.918195461 x = -3.918195461 Simplifying x = -3.918195461

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.168195461, -3.918195461}

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