(1+2sinxcosx)/(cos^2x-sin^2x)
=(cos^2x+sin^2x+2sinxcosx)/(cos^2x-sin^2x) (上下同除以cos^2x)
=(1+tan^2x+2tanx)/(1-tan^2x)
=(1+tanx)^2/([(1-tanx)(1+tanx)]
=(1+tanx)/(1-tanx)