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