x^4-8*x^2-72=0

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Solution for x^4-8*x^2-72=0 equation:


Simplifying
x4 + -8x2 + -72 = 0

Reorder the terms:
-72 + -8x2 + x4 = 0

Solving
-72 + -8x2 + 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 + -8x2 + 72 + x4 = 0 + 72

Reorder the terms:
-72 + 72 + -8x2 + x4 = 0 + 72

Combine like terms: -72 + 72 = 0
0 + -8x2 + x4 = 0 + 72
-8x2 + x4 = 0 + 72

Combine like terms: 0 + 72 = 72
-8x2 + x4 = 72

The x term is -8x2.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8x2 + 16 + x4 = 72 + 16

Reorder the terms:
16 + -8x2 + x4 = 72 + 16

Combine like terms: 72 + 16 = 88
16 + -8x2 + x4 = 88

Factor a perfect square on the left side:
(x2 + -4)(x2 + -4) = 88

Calculate the square root of the right side: 9.38083152

Break this problem into two subproblems by setting 
(x2 + -4) equal to 9.38083152 and -9.38083152.

Subproblem 1

x2 + -4 = 9.38083152 Simplifying x2 + -4 = 9.38083152 Reorder the terms: -4 + x2 = 9.38083152 Solving -4 + x2 = 9.38083152 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + x2 = 9.38083152 + 4 Combine like terms: -4 + 4 = 0 0 + x2 = 9.38083152 + 4 x2 = 9.38083152 + 4 Combine like terms: 9.38083152 + 4 = 13.38083152 x2 = 13.38083152 Simplifying x2 = 13.38083152 Take the square root of each side: x = {-3.657981892, 3.657981892}

Subproblem 2

x2 + -4 = -9.38083152 Simplifying x2 + -4 = -9.38083152 Reorder the terms: -4 + x2 = -9.38083152 Solving -4 + x2 = -9.38083152 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + x2 = -9.38083152 + 4 Combine like terms: -4 + 4 = 0 0 + x2 = -9.38083152 + 4 x2 = -9.38083152 + 4 Combine like terms: -9.38083152 + 4 = -5.38083152 x2 = -5.38083152 Simplifying x2 = -5.38083152 Reorder the terms: 5.38083152 + x2 = -5.38083152 + 5.38083152 Combine like terms: -5.38083152 + 5.38083152 = 0.00000000 5.38083152 + 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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