Nearly there with this problem, but need a nudge to the finish!
Prove that is a factor of and write down two other factors of the expression. Hence factorize the expression completely.
Then since is a factor(Factor theorem)
And substituting , proves is a factor.
Similarly (a - b) and (c - a) are the other factors.
So by factor theorem,
How do I find out Factor 4?
Thanks for your help.