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

в) cos(13π/6)=cos(2π+π/6)=cos(π/6)=√3/2
 г) ctg(7π/4)=ctg(2π-π/4)=-ctg(π/4)=-1