Exercise
The representative of degree smaller than 5 for the class of the element X6 in the residue class ring Q[X]/(X5 - 1) is
0
1
X
No.
No.
Yes,
if a is the class of X modulo X5 - 1,
then we compute
a6 = a · a5 =
a · 1 = a.
But a representative for a is X.