x^4-2x^2-81=0

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


Simplifying
x4 + -2x2 + -81 = 0

Reorder the terms:
-81 + -2x2 + x4 = 0

Solving
-81 + -2x2 + x4 = 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 + -2x2 + 81 + x4 = 0 + 81

Reorder the terms:
-81 + 81 + -2x2 + x4 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + -2x2 + x4 = 0 + 81
-2x2 + x4 = 0 + 81

Combine like terms: 0 + 81 = 81
-2x2 + x4 = 81

The x term is -2x2.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2x2 + 1 + x4 = 81 + 1

Reorder the terms:
1 + -2x2 + x4 = 81 + 1

Combine like terms: 81 + 1 = 82
1 + -2x2 + x4 = 82

Factor a perfect square on the left side:
(x2 + -1)(x2 + -1) = 82

Calculate the square root of the right side: 9.055385138

Break this problem into two subproblems by setting 
(x2 + -1) equal to 9.055385138 and -9.055385138.

Subproblem 1

x2 + -1 = 9.055385138 Simplifying x2 + -1 = 9.055385138 Reorder the terms: -1 + x2 = 9.055385138 Solving -1 + x2 = 9.055385138 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + x2 = 9.055385138 + 1 Combine like terms: -1 + 1 = 0 0 + x2 = 9.055385138 + 1 x2 = 9.055385138 + 1 Combine like terms: 9.055385138 + 1 = 10.055385138 x2 = 10.055385138 Simplifying x2 = 10.055385138 Take the square root of each side: x = {-3.171022727, 3.171022727}

Subproblem 2

x2 + -1 = -9.055385138 Simplifying x2 + -1 = -9.055385138 Reorder the terms: -1 + x2 = -9.055385138 Solving -1 + x2 = -9.055385138 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + x2 = -9.055385138 + 1 Combine like terms: -1 + 1 = 0 0 + x2 = -9.055385138 + 1 x2 = -9.055385138 + 1 Combine like terms: -9.055385138 + 1 = -8.055385138 x2 = -8.055385138 Simplifying x2 = -8.055385138 Reorder the terms: 8.055385138 + x2 = -8.055385138 + 8.055385138 Combine like terms: -8.055385138 + 8.055385138 = 0.000000000 8.055385138 + x2 = 0.000000000 The solution to this equation could not be determined.This subproblem is being ignored because a solution could not be determined. The solution to this equation could not be determined.

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