x^2-5x-81=0

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


Simplifying
x2 + -5x + -81 = 0

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

Solving
-81 + -5x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '81' to each side of the equation.
-81 + -5x + 81 + x2 = 0 + 81

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

Combine like terms: -81 + 81 = 0
0 + -5x + x2 = 0 + 81
-5x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
-5x + x2 = 81

The x term is -5x.  Take half its coefficient (-2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
-5x + 6.25 + x2 = 81 + 6.25

Reorder the terms:
6.25 + -5x + x2 = 81 + 6.25

Combine like terms: 81 + 6.25 = 87.25
6.25 + -5x + x2 = 87.25

Factor a perfect square on the left side:
(x + -2.5)(x + -2.5) = 87.25

Calculate the square root of the right side: 9.340770846

Break this problem into two subproblems by setting 
(x + -2.5) equal to 9.340770846 and -9.340770846.


Subproblem 1
x + -2.5 = 9.340770846

Simplifying
x + -2.5 = 9.340770846

Reorder the terms:
-2.5 + x = 9.340770846

Solving
-2.5 + x = 9.340770846

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '2.5' to each side of the equation.
-2.5 + 2.5 + x = 9.340770846 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + x = 9.340770846 + 2.5
x = 9.340770846 + 2.5

Combine like terms: 9.340770846 + 2.5 = 11.840770846
x = 11.840770846

Simplifying
x = 11.840770846


Subproblem 2
x + -2.5 = -9.340770846

Simplifying
x + -2.5 = -9.340770846

Reorder the terms:
-2.5 + x = -9.340770846

Solving
-2.5 + x = -9.340770846

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '2.5' to each side of the equation.
-2.5 + 2.5 + x = -9.340770846 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + x = -9.340770846 + 2.5
x = -9.340770846 + 2.5

Combine like terms: -9.340770846 + 2.5 = -6.840770846
x = -6.840770846

Simplifying
x = -6.840770846


Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {11.840770846, -6.840770846}

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