Найдите значение sin (φ+30) если cos φ=1/3

180<φ<270

Cos α = - 1/3

sin² α = 1 - cos²α = 1 - 1/9 = 8/9

sin α = - 2√2 / 3

sin (α + 30°) = sin α·cos 30° + cos α·sin 30° = - 2√2 / 3 · √3/2 + ( - 1/3) ·1/2 =

= - 2√6 / 6 - 1/6 = - (2√6 + 1) / 6