Вычислите функции:

a) sin (-13π/4)

б) tg (-19π/6)

в) cos (13π/6) г) ctg (7π/4)

a) sin (-13π/4) = - sin (13π/4) = - sin (2π+π+π/4) = - sin (π+π/4) = sin (π/4) = √2/2

б) tg (-19π/6) = - tg (19 π/6) = - tg (2π+π+π/6) = - tg (π+π/6) = tg (π/6) = 1/√3

в) cos (13π/6) = cos (2 π+π/6) = cos (π/6) = √3/2

г) ctg (7π/4) = ctg (2 π-π/4) = - ctg (π/4) = - 1