x^4-3x^2-72=0

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Solution for x^4-3x^2-72=0 equation:


Simplifying
x4 + -3x2 + -72 = 0

Reorder the terms:
-72 + -3x2 + x4 = 0

Solving
-72 + -3x2 + x4 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '72' to each side of the equation.
-72 + -3x2 + 72 + x4 = 0 + 72

Reorder the terms:
-72 + 72 + -3x2 + x4 = 0 + 72

Combine like terms: -72 + 72 = 0
0 + -3x2 + x4 = 0 + 72
-3x2 + x4 = 0 + 72

Combine like terms: 0 + 72 = 72
-3x2 + x4 = 72

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 = 72 + 2.25

Reorder the terms:
2.25 + -3x2 + x4 = 72 + 2.25

Combine like terms: 72 + 2.25 = 74.25
2.25 + -3x2 + x4 = 74.25

Factor a perfect square on the left side:
(x2 + -1.5)(x2 + -1.5) = 74.25

Calculate the square root of the right side: 8.61684397

Break this problem into two subproblems by setting 
(x2 + -1.5) equal to 8.61684397 and -8.61684397.

Subproblem 1

x2 + -1.5 = 8.61684397 Simplifying x2 + -1.5 = 8.61684397 Reorder the terms: -1.5 + x2 = 8.61684397 Solving -1.5 + x2 = 8.61684397 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 = 8.61684397 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x2 = 8.61684397 + 1.5 x2 = 8.61684397 + 1.5 Combine like terms: 8.61684397 + 1.5 = 10.11684397 x2 = 10.11684397 Simplifying x2 = 10.11684397 Take the square root of each side: x = {-3.180698661, 3.180698661}

Subproblem 2

x2 + -1.5 = -8.61684397 Simplifying x2 + -1.5 = -8.61684397 Reorder the terms: -1.5 + x2 = -8.61684397 Solving -1.5 + x2 = -8.61684397 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 = -8.61684397 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x2 = -8.61684397 + 1.5 x2 = -8.61684397 + 1.5 Combine like terms: -8.61684397 + 1.5 = -7.11684397 x2 = -7.11684397 Simplifying x2 = -7.11684397 Reorder the terms: 7.11684397 + x2 = -7.11684397 + 7.11684397 Combine like terms: -7.11684397 + 7.11684397 = 0.00000000 7.11684397 + x2 = 0.00000000 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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