Thread: express sin x/2 in terms of cos x

express sin x/2 in terms of cos x

I have the answer, but how would you approach this problem?

Thanks.

Originally Posted by white_cap

express sin x/2 in terms of cos x

I have the answer, but how would you approach this problem?

Thanks.

use the half angle formula. you know it right?

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?

Originally Posted by white_cap

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)