#sin(x+y)/cos(x-y)-2tan(x+y)#
#=((sinxcosy)/(cosxcosy)+(cosxsiny)/(cosxcosy))/((cosxcosy)/(cosxcosy)+(sinxsiny)/(cosxcosy))
-2tan(x+y)#
#=(tanx+tany)/(1+tanxtany)-(2(tanx+tany))/(1-tanxtany)#
#=(((tanx+tany)(1-tanxtany-2-2tanxtany))/(1-tan^2xtan^2y))#
#=((tanx+tany)(-1-3tanxtany))/(1-tan^2xtan^2y)#
#=((tanx+tany)(1+3tanxtany))/(tan^2xtan^2y-1)#