Some videos I've made

Prerequisite for addition formula: https://www.youtube.com/watch?v=iHZmi2MHqWc

Proof of formula for sin(A+B):  https://www.youtube.com/watch?v=BEETggUVMrY

Proof of formula for cos(A+B):  https://www.youtube.com/watch?v=gTpNnlRxnIY

Proof of formula for tan(A+B):  https://www.youtube.com/watch?v=D5VJiL0DMWU

Some C3 Trig stuff: https://www.youtube.com/watch?v=Gcby6WYAVKg

The product rule proof with limits:https://www.youtube.com/watch?v=9FRFRVTUthk