3x^4+18=21x^2

Solution for 3x^4+18=21x^2 equation:

Simplifying
3x4 + 18 = 21x2

Reorder the terms:
18 + 3x4 = 21x2

Solving
18 + 3x4 = 21x2

Solving for variable 'x'.

Reorder the terms:
18 + -21x2 + 3x4 = 21x2 + -21x2

Combine like terms: 21x2 + -21x2 = 0
18 + -21x2 + 3x4 = 0

Factor out the Greatest Common Factor (GCF), '3'.
3(6 + -7x2 + x4) = 0

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

Factor a difference between two squares.
3(((1 + x)(1 + -1x))(6 + -1x2)) = 0

Ignore the factor 3.
Subproblem 1
Set the factor '(6 + -1x2)' equal to zero and attempt to solve:

Simplifying
6 + -1x2 = 0

Solving
6 + -1x2 = 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 + -1x2 = 0 + -6

Combine like terms: 6 + -6 = 0
0 + -1x2 = 0 + -6
-1x2 = 0 + -6

Combine like terms: 0 + -6 = -6
-1x2 = -6

Divide each side by '-1'.
x2 = 6

Simplifying
x2 = 6

Take the square root of each side:
x = {-2.449489743, 2.449489743}
Subproblem 2
Set the factor '(1 + x)' equal to zero and attempt to solve:

Simplifying
1 + x = 0

Solving
1 + x = 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 + x = 0 + -1

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

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

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

Simplifying
1 + -1x = 0

Solving
1 + -1x = 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 + -1x = 0 + -1

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

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

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

Simplifying
x = 1
Solution
x = {-2.449489743, 2.449489743, -1, 1}