Trigonometric Identities

The times they are a-changin’.

This post seems to be older than 14 years—a long time on the internet. It might be outdated.

Wikipedia has a list of trig identities.

I’m not quite sure what’s worse, the fact that Wikipedia has them or the fact that I need to use them.

Calc III exam at 7:30 6:30.

Here are the three I’ve been using a lot:

  • Sin2[x] = (1-Cos[2x])/2
  • Cos2[x] = (1+Cos[2x])/2
  • Sin2[x] + Cos2[x] = 1



2 thoughts on “Trigonometric Identities”

  1. On the plus side, the third is just the Pythagorean Theorem, which you should have thoroughly memorized, and either of the other two rolls into the other. Fun stuff. And thanks for the list.

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