Ta có:
$\begin{array}{l}sin^2M + cos^2M = 1\\ \Rightarrow cos^2M = 1 - sin^2M = 1 -0,8^2 = 0,36\\ \Rightarrow cosM = \sqrt{0,36} = 0,6\\ \Rightarrow tanM = \dfrac{sinM}{cosM} = \dfrac{0,8}{0,6} = \dfrac{4}{3}\\ \Rightarrow cotM = \dfrac{1}{tanM} = \dfrac{3}{4}\end{array}$