Tgα=8 (8/17)
1+tg²α=1/cos²α
1+(8 8/17)²=1/cos²α
(8 8/17)²=(144/17)²=20736/289
1+20736/289=21025/289
1/cos²α=21025/289
cos²α=289/21025
sin²α+cos²α=1
sin²α+289/21025=1
sin²α=20736/21025
sinα=√(20736/21025)
sinα=144/145
ctg(-600°)=-ctg600°=-ctg(720°-120°)=-ctg120°=-ctg(180°-60°)=-(-ctg60°)=ctg60°=1/√3=√3/3