1. cos (-7pi/3) 2. tg (10pi/3) 3. ctg (-9pi/4)

Представим значения аргументов тригонометрических функций в следующем виде:

-7π/3 = - 6π/3 - π/3 = - 2π - π/3;

10π/3 = 9π/3 + π/3 = 3π + π/3;

-9π/4 = - 8π/4 - π/4 = - 2π - π/4.

Тогда с учетом периодичности, получим:

1. cos (-2π - π/3) = cos (-π/3) = 1/2;

2. tg (3π + π/3) = tg (π/3) = √3;

3. ctg (-2π - π/4) = ctg (-π/4) = - 1.