Help computing with third roots of unity using Maple?

Question

I simply would like to compute
(a+r*b+r^2*c)^3
where r^3=1 is a principal third root of of 1.

I know the result, but like to compute it using maple.
expand and simplify and assume instructions simply does not work!

The Maple software is properly installed!

Answer 1

Its not properly installed