三角函数习题1.sin10*sin30*sin50*sin70等于多少啊 天才们
问答/456℃/2024-05-03 11:46:50
优质解答:
sin10*sin50*sin70=cos20cos40cos80
=sin20cos20cos40cos80/sin20
=1/2 sin40cos40cos80/sin20
=1/4 sin80cos80/sin20
=1/8 sin160/sin20
=1/8 sin20/sin20
=1/8
再乘以sin30°即:1/8*1/2=1/16