Posted by  on .
Show that tanx= (sinx/ cosx)
can be written as:
tan(xy) = (tanx  tany) / (1+ tanxtany)

adv functions 
Reiny,
write tan (xy)
= sin(xy)/cos(xy)
= [sinxcosy  cosxsiny[/[cosxcosy + sinxsiny]
Now divide everybody by cosxcosy and it will all fall into place.