SOLUTION: How do you factor x^4 - 3x^2 - 4

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: How do you factor x^4 - 3x^2 - 4      Log On


   

Question 20379: How do you factor x^4 - 3x^2 - 4
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
a little mental leap is required here.

Let y=x%5E2, so that y%5E2+=+x%5E4. Are these definitions OK?

Right, x%5E4+-+3x%5E2+-+4 then becomes y%5E2+-+3y+-+4 which is a normal quadratic that factorises easily to (y-4)(y+1).

Hence, we have %28x%5E2+-+4%29%28x%5E2+%2B+1%29

jon.