Originally Posted by

**Wolvenmoon** So, I know that from the sine, cosine, and tangent of a sum or difference I can figure out the double angle and half angle identities for a sine, cosine, and tangent.

I'm having trouble finding a pattern to memorize the tangent of a sum or difference, so I've done nothing with the tangents yet.

But I'm successfully able to figure out the double angle identities using the sum identities.

I haven't figured out what to do to get to the half angle identities from the sum or difference identities or the double angle identities.

So, is there any way to figure out the tangent of a sum or difference from the sine and cosine of a sum or difference, and is there a way to get to the half angle identities from the sum/difference identities?

Thanks!