[sin4α/(1+cos4α)][cos2α/(1+cos2α)]×[cosα/(1+cosα)]×{cos(α/2)/[1+cos(α/2)]}
=[2sin2αcos2α/2cos22α)× [cos2α/2cos2α)]×[cosα/2cos2（α/2)]×{cos(α/2)/[2cos2(α/4)]}
=【2sin2αcos2α×cos2α×cosα×cos(α/2)】/[2cos22α)×2cos2α×2cos2（α/2）×2cos2(α/4)】
=2sinαcosα/[8cosα×cos（α/2）×cos2(α/4)]
=2sin（α/2）/4cos2(α/4)=2sin(α/4)/[2cos(α/4)]=tan(α/4)
α≠4kπ+2π,2kπ+π,kπ+0.5π,0.5kπ+0.25π,k∈Z