1. ## Cos addition identity but with a multiplyier

i hope that someone can help, i have a equation that is in the form

cos(s)cos(t)–Asin(s)sin(t)

i want to simplify it using the simple trig identity

cos(s+t)=cos(s)cos(t)–sin(s)sin(t)

but i don't think that i can because of the A multiplying term, anyone know of another way that you can or if you defiantly can't
Cheers
WN

2. Without knowing the exact expression in question, it's hard to say for sure. But you could, I suppose, so something like the following:

. . . . .cos(s)cos(t) – Asin(s)sin(t) = [cos(s)cos(t) - sin(s)sin(t)] - (A - 1)sin(s)sin(t)

I don't know if that will help at all, though....

3. well attached is the whole equation
Cheers
WN