I’m one who really hates memorizing formulas, be in as a student or tutor. So I shall share how I remember the three very useful trigonometry identities. I’ll start with the one which you all definitely can identify with.

### Now how do we get the other 2?

Simply divide the above equation by and respectively.

Lets divide by !

Voila! we have

You can try to do the same with ! Let me know if you have problems!