Rút gọn biểu thức sau B= cos6·.cos12·.cos24·.cos48 ·

Ta có: `Bsin6^o = cos6^o*sin6^o*cos12^o*cos24^o*cos48^o`

`=1/2sin12^o*cos12^o*cos24^o*cos48^o`

`=1/4sin24^o*cos24^o*cos48^o`

`=1/8sin48^o*cos48^o`

`=1/16sin96^o`

`=1/16cos6^o`

`=>` `Bsin6^o = 1/16cos6^o`

`=>` `B = 1/16*(cos6^o)/(sin6^o)`

`=>` `B = (cot6^o)/16`

Vậy `B=(cot6^o)/16`