In Exercises 1-4, perform the addition or subtraction and use the fundamental identities to simplify. (There is more than one correct form of each answer.)
1. 1 / 1 + cos x + 1 / 1 - cos x
2. 1 / sec x + 1 - 1 / sec x - 1
3. cos x / 1 + sin x - cos x / 1 - sin x
4. sin x / 1 + cos x + sin x / 1 - cos x