[tan(pi/4+x)-tan(pi/4-x)]/[tan(pi/4+x)+tan(pi/4-x)]=2sinxcosx I tried to prove this trig identity but I an really stuck. I think tan of pi/4 is '1', and if I do that then my numerator becomes zero, thus zero=2sinxcosx. But that can't be right, so I don't know what to do now. LS= (1+tanx-1-tanx)/(1+tanx+1-tanx) I get 0=2sinxcosx Any thoughts? Also, I am wondering where this advanced formatting option is or how to do it.