I am pretty sure I'm almost done the first one.

#1

Use the identity for sin2x and an identity for cos2x to verify that

but when I use the formula for double angles like where with a

I think it is

Thanks for any help you may have.

And

#2

how do you find roots/solve something like

or I algebraically? I have done questions where you have to do proofs, but I have no examples like this from my teacher, thanks.

sorry about the multiple questions but the site was down lol.