∵积化和差公式 sinαcosβ=[sin(α+β)+sin(α-β)]/2sinαsinβ=-[cos(α+β)-cos(α-β)]/2∴sin70°cos20°-sin10°sin50°=[sin(70°+20°)+sin(70°-20°)]/2-{-[cos(10°+50°)-cos(10°-50°)]}/2=[sin90°+...