1，极限=lim(1-x)(sinπx/2)/(cosπx/2)=lim(1-x)/(cosπx/2)，用洛必达，=lim(-1)/(-π/2)(sinπx/2)=2/π2，极限=lim(sin3x)(cosx)/(cos3x)(sinx)=limsin3x/sinx=-1
