-x^4+8x^2-9=0

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Solution for -x^4+8x^2-9=0 equation:


Simplifying
-1x4 + 8x2 + -9 = 0

Reorder the terms:
-9 + 8x2 + -1x4 = 0

Solving
-9 + 8x2 + -1x4 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
9 + -8x2 + x4 = 0

Move the constant term to the right:

Add '-9' to each side of the equation.
9 + -8x2 + -9 + x4 = 0 + -9

Reorder the terms:
9 + -9 + -8x2 + x4 = 0 + -9

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

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

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 = -9 + 16

Reorder the terms:
16 + -8x2 + x4 = -9 + 16

Combine like terms: -9 + 16 = 7
16 + -8x2 + x4 = 7

Factor a perfect square on the left side:
(x2 + -4)(x2 + -4) = 7

Calculate the square root of the right side: 2.645751311

Break this problem into two subproblems by setting 
(x2 + -4) equal to 2.645751311 and -2.645751311.

Subproblem 1

x2 + -4 = 2.645751311 Simplifying x2 + -4 = 2.645751311 Reorder the terms: -4 + x2 = 2.645751311 Solving -4 + x2 = 2.645751311 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 = 2.645751311 + 4 Combine like terms: -4 + 4 = 0 0 + x2 = 2.645751311 + 4 x2 = 2.645751311 + 4 Combine like terms: 2.645751311 + 4 = 6.645751311 x2 = 6.645751311 Simplifying x2 = 6.645751311 Take the square root of each side: x = {-2.577935475, 2.577935475}

Subproblem 2

x2 + -4 = -2.645751311 Simplifying x2 + -4 = -2.645751311 Reorder the terms: -4 + x2 = -2.645751311 Solving -4 + x2 = -2.645751311 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 = -2.645751311 + 4 Combine like terms: -4 + 4 = 0 0 + x2 = -2.645751311 + 4 x2 = -2.645751311 + 4 Combine like terms: -2.645751311 + 4 = 1.354248689 x2 = 1.354248689 Simplifying x2 = 1.354248689 Take the square root of each side: x = {-1.163721912, 1.163721912}

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-2.577935475, 2.577935475, -1.163721912, 1.163721912}

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