7x^4-21x^2-5=0

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Solution for 7x^4-21x^2-5=0 equation:


Simplifying
7x4 + -21x2 + -5 = 0

Reorder the terms:
-5 + -21x2 + 7x4 = 0

Solving
-5 + -21x2 + 7x4 = 0

Solving for variable 'x'.

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

Divide each side by '7'.
-0.7142857143 + -3x2 + x4 = 0

Move the constant term to the right:

Add '0.7142857143' to each side of the equation.
-0.7142857143 + -3x2 + 0.7142857143 + x4 = 0 + 0.7142857143

Reorder the terms:
-0.7142857143 + 0.7142857143 + -3x2 + x4 = 0 + 0.7142857143

Combine like terms: -0.7142857143 + 0.7142857143 = 0.0000000000
0.0000000000 + -3x2 + x4 = 0 + 0.7142857143
-3x2 + x4 = 0 + 0.7142857143

Combine like terms: 0 + 0.7142857143 = 0.7142857143
-3x2 + x4 = 0.7142857143

The x term is -3x2.  Take half its coefficient (-1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
-3x2 + 2.25 + x4 = 0.7142857143 + 2.25

Reorder the terms:
2.25 + -3x2 + x4 = 0.7142857143 + 2.25

Combine like terms: 0.7142857143 + 2.25 = 2.9642857143
2.25 + -3x2 + x4 = 2.9642857143

Factor a perfect square on the left side:
(x2 + -1.5)(x2 + -1.5) = 2.9642857143

Calculate the square root of the right side: 1.721710113

Break this problem into two subproblems by setting 
(x2 + -1.5) equal to 1.721710113 and -1.721710113.

Subproblem 1

x2 + -1.5 = 1.721710113 Simplifying x2 + -1.5 = 1.721710113 Reorder the terms: -1.5 + x2 = 1.721710113 Solving -1.5 + x2 = 1.721710113 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + x2 = 1.721710113 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x2 = 1.721710113 + 1.5 x2 = 1.721710113 + 1.5 Combine like terms: 1.721710113 + 1.5 = 3.221710113 x2 = 3.221710113 Simplifying x2 = 3.221710113 Take the square root of each side: x = {-1.794912286, 1.794912286}

Subproblem 2

x2 + -1.5 = -1.721710113 Simplifying x2 + -1.5 = -1.721710113 Reorder the terms: -1.5 + x2 = -1.721710113 Solving -1.5 + x2 = -1.721710113 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + x2 = -1.721710113 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x2 = -1.721710113 + 1.5 x2 = -1.721710113 + 1.5 Combine like terms: -1.721710113 + 1.5 = -0.221710113 x2 = -0.221710113 Simplifying x2 = -0.221710113 Reorder the terms: 0.221710113 + x2 = -0.221710113 + 0.221710113 Combine like terms: -0.221710113 + 0.221710113 = 0.000000000 0.221710113 + x2 = 0.000000000 The solution to this equation could not be determined.This subproblem is being ignored because a solution could not be determined. The solution to this equation could not be determined.

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