Hey all, I could use some help with this problem:

Determine the intervals in which solutions are sure to exist:

$\displaystyle

(x-1)y\prime\prime\prime\prime + (x+1)y\prime\prime + (\tan x)y = 0

$

Not really sure how to approach this. What am I supposed to be doing?

**ETA**

Minutes after posting this, I figured it out, haaa. Divide all terms by (x-1) and that makes life easier.