Trignometry problem plz
no 3, 5 and 6

3. First factor as a difference of cubes:

For the remaining group, apply the double angle identity.

5. seems rather tricky. You might want to post another question for that problem alone...

6. Factorize the left side as a sum of cubes:

From here we have to prove that

We can write everything in terms of sine:

(double angle identity)

(angle sum identity)

After some simplifying, we're left with showing that

or

This last equality follows from what you could the triple angle identity for sine,