Is there a way to do this question using only double angle formulas? Our class has not done the half angle formula yet.
I googled the half angle formula, and it worked wonders. Thanks
So i'm assuming you can't do this with only the double angle formula?
yes, there is a way to use double angles.
Let , so now the problem is to express in terms of
start with the double angle formula for cosine:
now solve for , when you're finished, replace all the 's with and viola! (you'll realize this is just the half angle formula. your sly professor just had you derive it yourself)