15x^4-3x^2-18=0

Solution for 15x^4-3x^2-18=0 equation:

Simplifying
15x4 + -3x2 + -18 = 0

Reorder the terms:
-18 + -3x2 + 15x4 = 0

Solving
-18 + -3x2 + 15x4 = 0

Solving for variable 'x'.

Factor out the Greatest Common Factor (GCF), '3'.
3(-6 + -1x2 + 5x4) = 0

Factor a trinomial.
3((-1 + -1x2)(6 + -5x2)) = 0

Ignore the factor 3.
Subproblem 1
Set the factor '(-1 + -1x2)' equal to zero and attempt to solve:

Simplifying
-1 + -1x2 = 0

Solving
-1 + -1x2 = 0

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

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

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

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

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

Simplifying
x2 = -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 '(6 + -5x2)' equal to zero and attempt to solve:

Simplifying
6 + -5x2 = 0

Solving
6 + -5x2 = 0

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

Add '-6' to each side of the equation.
6 + -6 + -5x2 = 0 + -6

Combine like terms: 6 + -6 = 0
0 + -5x2 = 0 + -6
-5x2 = 0 + -6

Combine like terms: 0 + -6 = -6
-5x2 = -6

Divide each side by '-5'.
x2 = 1.2

Simplifying
x2 = 1.2

Take the square root of each side:
x = {-1.095445115, 1.095445115}
Solution
x = {-1.095445115, 1.095445115}