Hi Grandad, Thanks for responding.
I did know those formulas and have been trying to work with them. I don't understand how you got the bottom on the right side to be that?
As far as I knew,
I thought that sin (a-b) could only be changed into sinacosb-sinbcosa using the sum and difference identities...
Am I missing something?
Don't confuse this with . That's a different formula altogether (although it is one of the ones that is used to derive the Sum to Product formulae).