Hello, i am in a grade 12 advanced functions class (i guess it's pretty much a pre-calc class) and we're doing double angle formulas and i don't get it at all. Teacher isn't a calculus teacher so she can't explain it very well. Anywho, my question is:

Use a double angle formula to rewrite:

cos2(2x)

What i did was just times it out and got:

cos4x

But i don't know what i'm doing....

please help.