z=1 is obviously a solution of , so z–1 is a factor. Divide by it to find the other factor.

The other four solutions of are the complex fifth roots of 1. So the values of θ will be 2kπ/5, for k=1,2,3,4.

This quartic polynomial should be the 'other factor" that you found in part a). So you know its zeros (from part b)) and therefore you know its (complex) linear factors. Pair these off into two complex conjugate pairs. The product of two complex conjugate complex linear factors will be a quadratic real factor.