a) \(cosB=0,8\Leftrightarrow\dfrac{AB}{BC}=0,8\Leftrightarrow AB=0,8.BC=0,8.10=8\left(cm\right)\)
Theo định lý Pitago:
\(AC=\sqrt{BC^2-AB^2}=\sqrt{10^2-8^2}=6\left(cm\right)\)
b) \(cosC=\dfrac{AC}{BC}=\dfrac{6}{10}=0,6\)
\(sinC=\dfrac{AB}{BC}=\dfrac{8}{10}=0.8\)
\(tanC=\dfrac{AB}{AC}=\dfrac{8}{6}=\dfrac{4}{3}\)
\(cotgC=\dfrac{1}{tanC}=\dfrac{3}{4}\)