8x^4-9x^2=18

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Solution for 8x^4-9x^2=18 equation:


Simplifying
8x4 + -9x2 = 18

Reorder the terms:
-9x2 + 8x4 = 18

Solving
-9x2 + 8x4 = 18

Solving for variable 'x'.

Reorder the terms:
-18 + -9x2 + 8x4 = 18 + -18

Combine like terms: 18 + -18 = 0
-18 + -9x2 + 8x4 = 0

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

Divide each side by '8'.
-2.25 + -1.125x2 + x4 = 0

Move the constant term to the right:

Add '2.25' to each side of the equation.
-2.25 + -1.125x2 + 2.25 + x4 = 0 + 2.25

Reorder the terms:
-2.25 + 2.25 + -1.125x2 + x4 = 0 + 2.25

Combine like terms: -2.25 + 2.25 = 0.00
0.00 + -1.125x2 + x4 = 0 + 2.25
-1.125x2 + x4 = 0 + 2.25

Combine like terms: 0 + 2.25 = 2.25
-1.125x2 + x4 = 2.25

The x term is -1.125x2.  Take half its coefficient (-0.5625).
Square it (0.31640625) and add it to both sides.

Add '0.31640625' to each side of the equation.
-1.125x2 + 0.31640625 + x4 = 2.25 + 0.31640625

Reorder the terms:
0.31640625 + -1.125x2 + x4 = 2.25 + 0.31640625

Combine like terms: 2.25 + 0.31640625 = 2.56640625
0.31640625 + -1.125x2 + x4 = 2.56640625

Factor a perfect square on the left side:
(x2 + -0.5625)(x2 + -0.5625) = 2.56640625

Calculate the square root of the right side: 1.602000702

Break this problem into two subproblems by setting 
(x2 + -0.5625) equal to 1.602000702 and -1.602000702.

Subproblem 1

x2 + -0.5625 = 1.602000702 Simplifying x2 + -0.5625 = 1.602000702 Reorder the terms: -0.5625 + x2 = 1.602000702 Solving -0.5625 + x2 = 1.602000702 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5625' to each side of the equation. -0.5625 + 0.5625 + x2 = 1.602000702 + 0.5625 Combine like terms: -0.5625 + 0.5625 = 0.0000 0.0000 + x2 = 1.602000702 + 0.5625 x2 = 1.602000702 + 0.5625 Combine like terms: 1.602000702 + 0.5625 = 2.164500702 x2 = 2.164500702 Simplifying x2 = 2.164500702 Take the square root of each side: x = {-1.471224219, 1.471224219}

Subproblem 2

x2 + -0.5625 = -1.602000702 Simplifying x2 + -0.5625 = -1.602000702 Reorder the terms: -0.5625 + x2 = -1.602000702 Solving -0.5625 + x2 = -1.602000702 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5625' to each side of the equation. -0.5625 + 0.5625 + x2 = -1.602000702 + 0.5625 Combine like terms: -0.5625 + 0.5625 = 0.0000 0.0000 + x2 = -1.602000702 + 0.5625 x2 = -1.602000702 + 0.5625 Combine like terms: -1.602000702 + 0.5625 = -1.039500702 x2 = -1.039500702 Simplifying x2 = -1.039500702 Reorder the terms: 1.039500702 + x2 = -1.039500702 + 1.039500702 Combine like terms: -1.039500702 + 1.039500702 = 0.000000000 1.039500702 + 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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