sin165度×cos15度=sin15×cos15=1/2 2sin15cos15=1/2 sin30=1/2 ×1/2=1/4
sin165cos15=sin(180-15)cos15=sin15cos15=sin30/2=(1/2)/2=1/4
sin165°×cos15°=sin15°×cos15°=sin30°/2=1/4
