(x^4)-(8x^2)-20=0

Solution for (x^4)-(8x^2)-20=0 equation:

Simplifying
(x4) + -1(8x2) + -20 = 0
x4 + -1(8x2) + -20 = 0

Remove parenthesis around (8x2)
x4 + -1 * 8x2 + -20 = 0

Multiply -1 * 8
x4 + -8x2 + -20 = 0

Reorder the terms:
-20 + -8x2 + x4 = 0

Solving
-20 + -8x2 + x4 = 0

Solving for variable 'x'.

Factor a trinomial.
(-2 + -1x2)(10 + -1x2) = 0

Subproblem 1
Set the factor '(-2 + -1x2)' equal to zero and attempt to solve:

Simplifying
-2 + -1x2 = 0

Solving
-2 + -1x2 = 0

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

Add '2' to each side of the equation.
-2 + 2 + -1x2 = 0 + 2

Combine like terms: -2 + 2 = 0
0 + -1x2 = 0 + 2
-1x2 = 0 + 2

Combine like terms: 0 + 2 = 2
-1x2 = 2

Divide each side by '-1'.
x2 = -2

Simplifying
x2 = -2

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 '(10 + -1x2)' equal to zero and attempt to solve:

Simplifying
10 + -1x2 = 0

Solving
10 + -1x2 = 0

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

Add '-10' to each side of the equation.
10 + -10 + -1x2 = 0 + -10

Combine like terms: 10 + -10 = 0
0 + -1x2 = 0 + -10
-1x2 = 0 + -10

Combine like terms: 0 + -10 = -10
-1x2 = -10

Divide each side by '-1'.
x2 = 10

Simplifying
x2 = 10

Take the square root of each side:
x = {-3.16227766, 3.16227766}
Solution
x = {-3.16227766, 3.16227766}