#### tashadewan

##### New member

- Joined
- May 30, 2005

- Messages
- 2

Write cos 3A in terms of cos A....i tried but i always wind up wit some sin in it n i dont know wht to do wit it.

the second one im having a terrible time wit is tan(x+y)tan(x-y)=[sin^2x-sin^2y]/[cos^2x-sin^2y]

i cant prove this...im stuck...theres a difference of squares in it but i cant figure out where to go from tehre

the last question is...how do i find the critical number for s=2sint+sin2t.

I found the derivative to be 2cos t +2cos 2t but i cant solve for 0 coz i dont know how to.....