cos20°cos70°sin50°=?
问题描述：
cos20°cos70°sin50°=?
答
=cos20sin20sin50=1/2 sin40sin50 =1/2sin40cos40=1/4sin80
(“sin20”指“sin二十度”我不会打)
答
1/2cos40
答
=cos20sin20si50
=0.5sin40sin50
=0.5sin40cos40
=0.25sin80
=0.25cos10