math people, I need your help (specifically people who are good at trig)

[Shooters]

Okay, I have this expression:

cos(At + Bt) - cos(At)

and I need to get it into the form:

sin(Bt)sin(2At + Bt)

Given the info that B/A << 1

I've tried using a a couple of trig identities, but I just can't seem to get it to work. By the way, this isn't for a math class. I need it to solve a dynamics problem.

 

[Mday]

this does not appear to work...

i used my graphing calculator...

set A to be 1000000 or so, and B to be 1, and graphed the 2 functions.

i recieved different graphs, and values for the 2 functions.

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double check what you typed, and attempt adding and subtracting the same term to see if you can collect values, and factor and junk.