In order to prove an identity one must have both sides of the identity...

If a) is

then you should know this. Hint: What are the definitions of tan(x), cot(x), sec(x), and csc(x)?

b) This is one side of a "standard" identity. Look at the link in your other thread and you should find it.

c) This is not so much of an identity as it is a simplification.

So what are sin(-a) and cos(-a)?

d)

How do you find ?

e) Hint: What is the form for tan(a + b)? (See that link again.)

-Dan