X^4-9X^2-81=0

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Solution for X^4-9X^2-81=0 equation:


Simplifying
X4 + -9X2 + -81 = 0

Reorder the terms:
-81 + -9X2 + X4 = 0

Solving
-81 + -9X2 + 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 + -9X2 + 81 + X4 = 0 + 81

Reorder the terms:
-81 + 81 + -9X2 + X4 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + -9X2 + X4 = 0 + 81
-9X2 + X4 = 0 + 81

Combine like terms: 0 + 81 = 81
-9X2 + X4 = 81

The X term is -9X2.  Take half its coefficient (-4.5).
Square it (20.25) and add it to both sides.

Add '20.25' to each side of the equation.
-9X2 + 20.25 + X4 = 81 + 20.25

Reorder the terms:
20.25 + -9X2 + X4 = 81 + 20.25

Combine like terms: 81 + 20.25 = 101.25
20.25 + -9X2 + X4 = 101.25

Factor a perfect square on the left side:
(X2 + -4.5)(X2 + -4.5) = 101.25

Calculate the square root of the right side: 10.062305899

Break this problem into two subproblems by setting 
(X2 + -4.5) equal to 10.062305899 and -10.062305899.

Subproblem 1

X2 + -4.5 = 10.062305899 Simplifying X2 + -4.5 = 10.062305899 Reorder the terms: -4.5 + X2 = 10.062305899 Solving -4.5 + X2 = 10.062305899 Solving for variable 'X'. Move all terms containing X to the left, all other terms to the right. Add '4.5' to each side of the equation. -4.5 + 4.5 + X2 = 10.062305899 + 4.5 Combine like terms: -4.5 + 4.5 = 0.0 0.0 + X2 = 10.062305899 + 4.5 X2 = 10.062305899 + 4.5 Combine like terms: 10.062305899 + 4.5 = 14.562305899 X2 = 14.562305899 Simplifying X2 = 14.562305899 Take the square root of each side: X = {-3.816058949, 3.816058949}

Subproblem 2

X2 + -4.5 = -10.062305899 Simplifying X2 + -4.5 = -10.062305899 Reorder the terms: -4.5 + X2 = -10.062305899 Solving -4.5 + X2 = -10.062305899 Solving for variable 'X'. Move all terms containing X to the left, all other terms to the right. Add '4.5' to each side of the equation. -4.5 + 4.5 + X2 = -10.062305899 + 4.5 Combine like terms: -4.5 + 4.5 = 0.0 0.0 + X2 = -10.062305899 + 4.5 X2 = -10.062305899 + 4.5 Combine like terms: -10.062305899 + 4.5 = -5.562305899 X2 = -5.562305899 Simplifying X2 = -5.562305899 Reorder the terms: 5.562305899 + X2 = -5.562305899 + 5.562305899 Combine like terms: -5.562305899 + 5.562305899 = 0.000000000 5.562305899 + 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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