Theoretical computer science. Please help

Prove that the following langauges are not regular (a) L = {ww: w element of {a, b}^*} (b) L = {a^nb^k: n greaterthanorequalto k} (c) L = {a^nb^mc^k:n + m > k > 0} (d) L = {w element of {a, b}^*: 2n_a(w) = 3n_b{w)} (e) L = {w element of {a, b}^*: w^R notequalto w}