k^4-8k^2-9=0

Solution for k^4-8k^2-9=0 equation:

Simplifying
k4 + -8k2 + -9 = 0

Reorder the terms:
-9 + -8k2 + k4 = 0

Solving
-9 + -8k2 + k4 = 0

Solving for variable 'k'.

Factor a trinomial.
(-1 + -1k2)(9 + -1k2) = 0

Factor a difference between two squares.
(-1 + -1k2)((3 + k)(3 + -1k)) = 0

Subproblem 1
Set the factor '(-1 + -1k2)' equal to zero and attempt to solve:

Simplifying
-1 + -1k2 = 0

Solving
-1 + -1k2 = 0

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

Add '1' to each side of the equation.
-1 + 1 + -1k2 = 0 + 1

Combine like terms: -1 + 1 = 0
0 + -1k2 = 0 + 1
-1k2 = 0 + 1

Combine like terms: 0 + 1 = 1
-1k2 = 1

Divide each side by '-1'.
k2 = -1

Simplifying
k2 = -1

The solution to this equation could not be determined.

This subproblem is being ignored because a solution could not be determined.
Subproblem 2
Set the factor '(3 + k)' equal to zero and attempt to solve:

Simplifying
3 + k = 0

Solving
3 + k = 0

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

Add '-3' to each side of the equation.
3 + -3 + k = 0 + -3

Combine like terms: 3 + -3 = 0
0 + k = 0 + -3
k = 0 + -3

Combine like terms: 0 + -3 = -3
k = -3

Simplifying
k = -3
Subproblem 3
Set the factor '(3 + -1k)' equal to zero and attempt to solve:

Simplifying
3 + -1k = 0

Solving
3 + -1k = 0

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

Add '-3' to each side of the equation.
3 + -3 + -1k = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -1k = 0 + -3
-1k = 0 + -3

Combine like terms: 0 + -3 = -3
-1k = -3

Divide each side by '-1'.
k = 3

Simplifying
k = 3
Solution
k = {-3, 3}