2. Let M be an R-module. (a) Show that HomR(M,) is a left-exact functor. (b) Show that M is projective if and only if HomR(M, :) is an exact functor. 2. Let M be an R-module. (a) Show that HomR(M,) is a left-exact functor. (b) Show that M is projective if and only if HomR(M, :) is an exact functor