3x^4-21x^2+1=0

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Solution for 3x^4-21x^2+1=0 equation:


Simplifying
3x4 + -21x2 + 1 = 0

Reorder the terms:
1 + -21x2 + 3x4 = 0

Solving
1 + -21x2 + 3x4 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
3 the coefficient of the squared term: 

Divide each side by '3'.
0.3333333333 + -7x2 + x4 = 0

Move the constant term to the right:

Add '-0.3333333333' to each side of the equation.
0.3333333333 + -7x2 + -0.3333333333 + x4 = 0 + -0.3333333333

Reorder the terms:
0.3333333333 + -0.3333333333 + -7x2 + x4 = 0 + -0.3333333333

Combine like terms: 0.3333333333 + -0.3333333333 = 0.0000000000
0.0000000000 + -7x2 + x4 = 0 + -0.3333333333
-7x2 + x4 = 0 + -0.3333333333

Combine like terms: 0 + -0.3333333333 = -0.3333333333
-7x2 + x4 = -0.3333333333

The x term is -7x2.  Take half its coefficient (-3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
-7x2 + 12.25 + x4 = -0.3333333333 + 12.25

Reorder the terms:
12.25 + -7x2 + x4 = -0.3333333333 + 12.25

Combine like terms: -0.3333333333 + 12.25 = 11.9166666667
12.25 + -7x2 + x4 = 11.9166666667

Factor a perfect square on the left side:
(x2 + -3.5)(x2 + -3.5) = 11.9166666667

Calculate the square root of the right side: 3.45205253

Break this problem into two subproblems by setting 
(x2 + -3.5) equal to 3.45205253 and -3.45205253.

Subproblem 1

x2 + -3.5 = 3.45205253 Simplifying x2 + -3.5 = 3.45205253 Reorder the terms: -3.5 + x2 = 3.45205253 Solving -3.5 + x2 = 3.45205253 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.5' to each side of the equation. -3.5 + 3.5 + x2 = 3.45205253 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x2 = 3.45205253 + 3.5 x2 = 3.45205253 + 3.5 Combine like terms: 3.45205253 + 3.5 = 6.95205253 x2 = 6.95205253 Simplifying x2 = 6.95205253 Take the square root of each side: x = {-2.636674521, 2.636674521}

Subproblem 2

x2 + -3.5 = -3.45205253 Simplifying x2 + -3.5 = -3.45205253 Reorder the terms: -3.5 + x2 = -3.45205253 Solving -3.5 + x2 = -3.45205253 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.5' to each side of the equation. -3.5 + 3.5 + x2 = -3.45205253 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x2 = -3.45205253 + 3.5 x2 = -3.45205253 + 3.5 Combine like terms: -3.45205253 + 3.5 = 0.04794747 x2 = 0.04794747 Simplifying x2 = 0.04794747 Take the square root of each side: x = {-0.218969107, 0.218969107}

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-2.636674521, 2.636674521, -0.218969107, 0.218969107}

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