Hello, I have this worksheet and there are a few problems I need clarification on. I've done most of them but my answers all turn out weird.

If cos(x) = -7/9, tan(x) < 0, find cos2(x)

Find all the solutions of sin5x + sinx = sin3x in the interval [0, 2pi)

Rewrite sin3xcos4y as a sum

Find all the solutions of 3cos(x/4) in the interval of [0, 2pi)

Thanks