sin70°×sin50°×sin30°×sin10°=cos20°×cos40°×(1/2)×sin10°=(1/2)×sin10°×cos20°×cos40°=(1/2)×sin10°×cos10°×cos20°×cos40°÷cos10°=(1/4)×2sin10°cos10°×cos20°×cos40°÷cos10...