tlnk bntu sy k kwn dngan prtanyaan sy yg di ats...tks yg sdh nau bntu

Mapel : Matematika
Kelas : X SMA
Bab : Trigonometri

Pembahasan :
Cos 105°
= Cos (180 - 75)°
= - Cos 75°
= - [Cos (45 + 30)°]
= - [Cos 45 Cos 30 - Sin 45 Sin 30]
= - [(1/2 √2)(1/2 √3) - (1/2 √2)(1/2)]
= - [1/4 √6 - 1/4 √2]
= 1/4 √2 - 1/4 √6
= 1/4 (√2 - √6)

Opsi C.