Welcome to Math Help Forum!Sum-to-Product formulas (and in #2 and #3, the double-angle formulae) together with basic factorising and simplifying techniques.
I'll start you off in each case, and leave you to try to complete it.
1)Now factorise by taking out a common factor . Then use the same sum-to-product formula again, and you're there.
2)Now re-arrange, and use the identity (twice), to write the expression in terms of and .
Factorise; cancel and you're there.
Let us know how you get on.