tg(13π/6)=tg(2π+(π/6))=tg(π/6)=1/√3;
ctg(13π/3)=ctg(4π+(π/3))=ctg(π/3)=1/√3;
tg(-17π/4)=tg(-4π-(π/4))=tg(-π/4)=-tg(π/4)=-1.
tg(13π/6)=tg(2π+(π/6))=tg(π/6)=1/√3;
ctg(13π/3)=ctg(4π+(π/3))=ctg(π/3)=1/√3;
tg(-17π/4)=tg(-4π-(π/4))=tg(-π/4)=-tg(π/4)=-1.