4. Prove the following Identities: sec 0 + tan 0 a) = tan 0 sec 0 b) 1- cos' x = sin x cot O + cos 0 1 + sin x c) 1- tan2 0 +1 = 2cos2 0 sec 0 1+ sin 0 1+ tan2 0 d) 1 - sin 0 cos' 0 e) 1-2cos' 0 = tan 0 - cot 0 sin O cos