How do I prove this an Identiy?:
((cos(a+b))/(cosa +sinb))=((cosa - sinb)/(cos(b-a)))

Please help. any help would be appreciated

Question

How do I prove this an Identiy?:
((cos(a+b))/(cosa +sinb))=((cosa - sinb)/(cos(b-a)))

Please help. any help would be appreciated

anonymous · Answer

what is cos(a+b) ?        and almost the same, what is   cos(b-a) ?

anonymous · Answer

cos(a+b)= (cosa)(cosb)-(sina)(sinb)
cos(b-a)= (cosb)(cosa)+(sinb)(sina)

anonymous · Answer

my proof isnt going where I thought it would, sorry

anonymous · Answer

thanks for trying

anonymous · Answer

please help

anonymous · Answer

(cos(a)+sin(b))x(cos(a)-sin(b))=cos^2(a)-sin^2(b)

and then use the cosxcosy=1/2 (cos(x-y)+cos(x+y)) identity to figure out what the other end comes out.
I can't guarantee it to work, but I think you should give it a try.

anonymous · Answer

I couldn't do it, but if you can simplify ((cos(a+b))/(cosa +sinb)) - ((cosa - sinb)/(cos(b-a))) down to 0, you will have your proof, just not in the right form. It is possible, but not for me (yet). Again, sorry I couldn't be more help.

anonymous · Answer

http://openstudy.com/updates/4f7990b7e4b0ddcbb89ec29f