(2) Let Z/nZ be the set of n elements {0, 1, 2, . . . , n ? 1}
with addition and multiplication modulo n. (a) Which element of
Z/5Z is the additive identity? Which element is the multiplicative
identity? For each nonzero element of Z/5Z, write out its
multiplicative inverse. (b) Prove that Z/nZ is a field if and only
if n is a prime number. [Hint: first work out why it’s not a field
when n isn’t prime....