Description: Mr. Chase blogs about math
Sparked by a conversation this past weekend about the usefulness of the half-angle identities, I constructed geometric proofs for and . Since I’ve never seen these anywhere before, I thought I’d share.
And while I was at it, I thought I’d share all my other geometric proofs, so here they are, posted mostly without comment.
Some of these are so well-known as to be not worth mentioning. Many of them have been stolen from Proofs Without Words I or Proofs Without Words II. I came up with a few of them myself. Frustratingly, almost none of them are to be found in Precalculus textbooks, where they might be learned and appreciated.