Distribute (FOIL) and simplify:
Use . We choose this one because our answer has cosines in it, and so we know we need to get rid of our sines.
Distribute the negative sign:
This is a question that Thelema asked me:
I don't have time to help at the moment so I'm asking if someone else can. Thanks!cos(s+t)cos(s-t)=cos^2s +cos^2t-1
so far i am at
[cos(s)cos(t)-sin(s)sin(t)][cos(s)cos(t)+sin(s)sin(t)] = cos^2(s)+cos^2(t)-1
I can multiply the left side but then i dont know
how to get it to equal the right. Can u plz help?