等式左边=2sinxcosx/[sinx+(cosx-1)][sinx-(cosx-1)]=2sinxcosx/[sin^2x-(cosx-1)^2]=2sinxcosx/(sin^2x-cos^2x+2cosx-1)=2sinxcosx/(2cosx-2cos^2x)=sinx/(1-cosx)=2sin(x/2)cos(x/2)/[1-2cos^2(x/2)+1]=sin(x/2)co...