This involves factoring from Vieta's Formulas:
The first step is to break a3+b3+c3 into 3r1r2r3+(r1+r2+r3)[r21+r22+r23−(r1r2+r2r3+r3r1).
The confusing part might be trying to find r21+r22+r23, yet we know that is equal to (r1+r2+r3)2−2(r1r2+r2r3+r3r1).
This can be better written as 3r1r2r3+(r1+r2+r3)[(r1+r2+r3)2−3(r1r2+r2r3+r3r1)].
Remember that r1,r2, and r3 are the roots of the polynomial which is an expression.
Note that r1+r2+r3=−ba , r1r2+r2r3+r3r1=ca, and r1r2r3=−da.
Try to plug the values in, and be careful and don't forget the x2 term.