SOLUTION: x^4 + radical 3 * x^2 - 3 = 0

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Question 352923: x^4 + radical 3 * x^2 - 3 = 0
Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
x%5E4+%2B+sqrt%283%29+%2A+x%5E2+-+3+=+0
The key to making this problem solvable is to recognize that the exponent on x%5E4 is twice as bug as the exponent on x%5E2. This makes your equation in "quadratic form" for x%5E2. So we can use techniques for solving quadratic equations to solve for x%5E2!

To make this process clearer, I am going to use a temporary variable. Let q = x%5E2. Then q%5E2+=+%28x%5E2%29%5E2+=+x%5E4. Substituting these into the equation we get:
q%5E2+%2B+sqrt%283%29%2Aq+-+3+=+0
This is clearly a quadratic equation. With the square root in there, factoring will not be easy. So we'll use the Quadratic formula:

Simplifying:
q+=+%28-sqrt%283%29+%2B-+sqrt%283+-+4%281%29%28-3%29%29%29%2F2%281%29
q+=+%28-sqrt%283%29+%2B-+sqrt%283+%2B12%29%29%2F2
q+=+%28-sqrt%283%29+%2B-+sqrt%2815%29%29%2F2
In long form:
q+=+%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2 or q+=+%28-sqrt%283%29+-+sqrt%2815%29%29%2F2
This is a solution for q. But we want a solution for x. So we substitute back in for q:
x%5E2+=+%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2 or x%5E2+=+%28-sqrt%283%29+-+sqrt%2815%29%29%2F2
Looking at the second equation above we see that the fraction is negative. But a negative numbers cannot be equal to something squared, like x%5E2! So unless you are looking for complex solutions, too, there are no solutions to the second equation. We are left with just the first equation:
x%5E2+=+%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2
To solve for x we just find the square root of each side:
sqrt%28x%5E2%29+=+sqrt%28%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2%29
abs%28x%29+=+sqrt%28%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2%29
x+=+0+%2B-+sqrt%28%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2%29
(Note: The zero is unnecessary mathematically. But Algebra.com's software will not let me use the "plus or minus" symbol without a number in front of it.)
In long form:
x+=+sqrt%28%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2%29 or x+=+-sqrt%28%28-sqrt%283%29+%2B+sqrt%2815%29%29%2F2%29

Eventually, after doing several of these "quadratic form"-type equations, you will be able to do these problems without a temporary variable. IOW, you will be able to straight from
x%5E4+%2B+sqrt%283%29+%2A+x%5E2+-+3+=+0
to