sin20sin30sin50sin70=?

sin20sin30sin50sin70=
0.5*2sin20sin30sin50sin70
=0.5sin50sin50sin70
=0.5*0.5*2*sin50sin50sin70
=0.25sin100sin70

sin20sin30sin50sin70
=1/2*2sin20cos20sin30sin50
=1/2sin40sin30sin50
=1/2*(1/2)*2sin40cos40sin30
=1/4sin80sin30
=1/8sin80

sin20sin30sin50sin70
=sin20*sin30*sin(20+30)*sin(20+20+30)
这个化简，我慢慢打！……

=0.5*sin20*sin(90-40)*sin(90-20)
=0.5*sin20*cos40*cos20
=0.5*sin20*cos(20*2)*cos20
……
这样解下去可不可以？

sin20sin30sin50sin70
=sin30*sin20*sin70*sin50
=0.5*sin20*cos20*cos40
=0.25*sin40*cos40
=0.125sin80