3x^4-16x^2-81=0

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Solution for 3x^4-16x^2-81=0 equation:


Simplifying
3x4 + -16x2 + -81 = 0

Reorder the terms:
-81 + -16x2 + 3x4 = 0

Solving
-81 + -16x2 + 3x4 = 0

Solving for variable 'x'.

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

Divide each side by '3'.
-27 + -5.333333333x2 + x4 = 0

Move the constant term to the right:

Add '27' to each side of the equation.
-27 + -5.333333333x2 + 27 + x4 = 0 + 27

Reorder the terms:
-27 + 27 + -5.333333333x2 + x4 = 0 + 27

Combine like terms: -27 + 27 = 0
0 + -5.333333333x2 + x4 = 0 + 27
-5.333333333x2 + x4 = 0 + 27

Combine like terms: 0 + 27 = 27
-5.333333333x2 + x4 = 27

The x term is -5.333333333x2.  Take half its coefficient (-2.666666667).
Square it (7.111111113) and add it to both sides.

Add '7.111111113' to each side of the equation.
-5.333333333x2 + 7.111111113 + x4 = 27 + 7.111111113

Reorder the terms:
7.111111113 + -5.333333333x2 + x4 = 27 + 7.111111113

Combine like terms: 27 + 7.111111113 = 34.111111113
7.111111113 + -5.333333333x2 + x4 = 34.111111113

Factor a perfect square on the left side:
(x2 + -2.666666667)(x2 + -2.666666667) = 34.111111113

Calculate the square root of the right side: 5.840471823

Break this problem into two subproblems by setting 
(x2 + -2.666666667) equal to 5.840471823 and -5.840471823.

Subproblem 1

x2 + -2.666666667 = 5.840471823 Simplifying x2 + -2.666666667 = 5.840471823 Reorder the terms: -2.666666667 + x2 = 5.840471823 Solving -2.666666667 + x2 = 5.840471823 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.666666667' to each side of the equation. -2.666666667 + 2.666666667 + x2 = 5.840471823 + 2.666666667 Combine like terms: -2.666666667 + 2.666666667 = 0.000000000 0.000000000 + x2 = 5.840471823 + 2.666666667 x2 = 5.840471823 + 2.666666667 Combine like terms: 5.840471823 + 2.666666667 = 8.50713849 x2 = 8.50713849 Simplifying x2 = 8.50713849 Take the square root of each side: x = {-2.916699931, 2.916699931}

Subproblem 2

x2 + -2.666666667 = -5.840471823 Simplifying x2 + -2.666666667 = -5.840471823 Reorder the terms: -2.666666667 + x2 = -5.840471823 Solving -2.666666667 + x2 = -5.840471823 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.666666667' to each side of the equation. -2.666666667 + 2.666666667 + x2 = -5.840471823 + 2.666666667 Combine like terms: -2.666666667 + 2.666666667 = 0.000000000 0.000000000 + x2 = -5.840471823 + 2.666666667 x2 = -5.840471823 + 2.666666667 Combine like terms: -5.840471823 + 2.666666667 = -3.173805156 x2 = -3.173805156 Simplifying x2 = -3.173805156 Reorder the terms: 3.173805156 + x2 = -3.173805156 + 3.173805156 Combine like terms: -3.173805156 + 3.173805156 = 0.000000000 3.173805156 + 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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