$$\eqalign{
& \Delta ABC\,\,vuong\,\,tai\,\,A \Rightarrow \angle B\,\,va\,\,\angle C\,\,la\,2\,\,goc\,\,phu\,\,nhau. \cr
& \Rightarrow \cos C = \sin B = 0,6 \cr
& \sin C = \sqrt {1 - {{\cos }^2}C} = \sqrt {1 - 0,{6^2}} = \sqrt {0,64} = 0,8 \cr
& \left( {Do\,\,\angle C < {{90}^0} \Rightarrow \sin C > 0} \right) \cr
& \Rightarrow \sin C = \cos B = 0,8 \cr
& \tan C = {{\sin C} \over {\cos C}} = {4 \over 3} = \cot B \cr
& \cot C = {1 \over {\tan C}} = {3 \over 4} = \tan B \cr} $$