Hey there!
What parts of the questions do you need help with? I'd be happy to provide you with a complete answer, but that ultimately won't help you in the long run. Can you please show us some working, then I'll be able to help with the parts you're stuck on. I'll drop a few hints though!
For the first one, I'd assume you're having trouble with the inductive step, since that's where most people go wrong. Try starting subbing in your assumption ASAP, then manipulate from there (may or may not be hard, havent actually tried it yet, doing it now so when you post up ur working, I can fully help
). For the second one, remember that volumes are calculated using the y squared, not the y. Think about it as y squared = cos x, then sub the values you need for the trapezoidal rule into that.