6) 2sin(-π/6 - π/6) + 3 + 7.5tg(-π/6) + 1cos(3π/2);

Решим по шагам: sin(-π/6 - π/6) = sin(-π/3) = -√3/2, tg(-π/6) = -1/√3, cos(3π/2) = 0. Выражение: 2(-√3/2) + 3 + 7.5(-1/√3) + 0 = -√3 + 3 - 2.5√3 = 3 - 3.5√3.