`sin6^o sin42^o sin66^o sin 78^o` dễ hiểu giúp e ạ

Đặt `B = sin6^osin42^osin66^osin78^o`

`=>` `Bcos6^o = cos6^osin6^osin42^osin66^osin78^o`

`=1/2sin12^ocos12^osin42^osin66^o`

`=1/4sin24^ocos24^osin42^o`

`=1/8sin48^ocos48^o`

`=1/16sin96^o`

`=1/16cos6^o`

`=>` `B = 1/16`