Originally Posted by

**Phire** Hi, how can I solve this by factoring:

x^4 + x - 18 = 0

I had thought that I could re-write it like this:

(x^2)^2 + x - 18 = 0

I'm not even sure if re-writing it that way helps. I was thinking I could also do this:

(x^2)^2 + x - 18 = 0

Replace (x^2) with y:

y^2 + y^(1/2) - 18 = 0

I still don't know if that would even help. I plugged the problem into an equation solving software and it said the only answer was 2 (unfortunately it doesn't explain how to solve it). By the way, if I use Descartes Rule of Signs, it says there should be a negative root (-x)^4 - x - 18. There is 1 sign change, but the software made no mention of another root. Did I use the rule of signs technique wrong?