Ta có : $\sin ^{2}C +\cos ^{2}C =1$

=>  $\cos ^{2}C =1-\sin ^{2}C =1-(0,8^{2})=0,36$

=>  $\cos C=0,6$

=>  $\tan C=\frac{\sin C}{\cos C}=\frac{0,8}{0,6}=\frac{4}{3}$

=>  $\cot C=\frac{\cos C}{\sin C}=\frac{0,6}{0,8}=\frac{3}{4}$