SOLUTION: how do you factor x^4 - X^2 - 20. I got (x^2+4)(x^2-5) but it is supposedly the wrong answer. Also tried x^2(x+1)(x-1)-20. still wrong.

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: how do you factor x^4 - X^2 - 20. I got (x^2+4)(x^2-5) but it is supposedly the wrong answer. Also tried x^2(x+1)(x-1)-20. still wrong.      Log On


   

Question 883719: how do you factor x^4 - X^2 - 20. I got (x^2+4)(x^2-5) but it is supposedly the wrong answer. Also tried x^2(x+1)(x-1)-20. still wrong.
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
X is a misprint.
Starting from x%5E4-x%5E2-20 try conveniently substituting like u=x%5E2 and rewrite the expression as u%5E2-u-20. You can take your guesses using 5 and 4 and hopefully find %28u%2B4%29%28u-5%29, and this obviously works ----- the expression using u.

Now substitute back for u:
highlight%28%28x%5E2%2B4%29%28x%5E2-5%29%29.
The answer key is wrong.
YOUR first result was correct.