x^2-8x-81=0

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Solution for x^2-8x-81=0 equation:


Simplifying
x2 + -8x + -81 = 0

Reorder the terms:
-81 + -8x + x2 = 0

Solving
-81 + -8x + 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 + -8x + 81 + x2 = 0 + 81

Reorder the terms:
-81 + 81 + -8x + x2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + -8x + x2 = 0 + 81
-8x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
-8x + x2 = 81

The x term is -8x.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8x + 16 + x2 = 81 + 16

Reorder the terms:
16 + -8x + x2 = 81 + 16

Combine like terms: 81 + 16 = 97
16 + -8x + x2 = 97

Factor a perfect square on the left side:
(x + -4)(x + -4) = 97

Calculate the square root of the right side: 9.848857802

Break this problem into two subproblems by setting 
(x + -4) equal to 9.848857802 and -9.848857802.

Subproblem 1

x + -4 = 9.848857802 Simplifying x + -4 = 9.848857802 Reorder the terms: -4 + x = 9.848857802 Solving -4 + x = 9.848857802 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + x = 9.848857802 + 4 Combine like terms: -4 + 4 = 0 0 + x = 9.848857802 + 4 x = 9.848857802 + 4 Combine like terms: 9.848857802 + 4 = 13.848857802 x = 13.848857802 Simplifying x = 13.848857802

Subproblem 2

x + -4 = -9.848857802 Simplifying x + -4 = -9.848857802 Reorder the terms: -4 + x = -9.848857802 Solving -4 + x = -9.848857802 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + x = -9.848857802 + 4 Combine like terms: -4 + 4 = 0 0 + x = -9.848857802 + 4 x = -9.848857802 + 4 Combine like terms: -9.848857802 + 4 = -5.848857802 x = -5.848857802 Simplifying x = -5.848857802

Solution

The solution to the problem is based on the solutions from the subproblems. x = {13.848857802, -5.848857802}

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