Nilai cos 75 + cos15

Cos 75+cos 15 
= cos(30+45)+cos(45-30) 
= cos 30.cos 45-sin 30.sin 45+cos 45.cos 30+sin 45.sin 30 
= 2cos 30.cos 45 
= 1.(akar 3)/2*(akar 2)/2 
= (akar 6)/4 (C)