nilai sin 105° + cos 15° adalah ?

jawab

sin 105  + cos 15 =
= sin(90+15) + cos 15
= cos 15+cos 15
= 2 cos 15
= 2 cos(45-30)
= 2 { cos 45 cos 30  + sin 45 sin 30}
= 2 {1/2 √2. 1/2 √3 + 1/2 √2 . 1/2}
= 2 (1/4 √6 + 1/4 √2)
= 2 (1/4)(√6 +√2)
= 1/2  (√6 + √2)