\(\dfrac{S_{ABC}}{S_{ANC}}=\dfrac{BC}{NC}=3\Rightarrow S_{ANC}=\dfrac{1}{3}\cdot240=80\left(cm^2\right)\\ \dfrac{S_{ANC}}{S_{MNC}}=\dfrac{AC}{MC}=\dfrac{5}{2}\Rightarrow S_{MNC}=\dfrac{2}{5}S_{ANC}=32\left(cm^2\right)\\ \Rightarrow S_{AMNB}=S_{ABC}-S_{MNC}=240-32=208\left(cm^2\right)\)
Áp dụng Menelaus cho tam giác ANC và cát tuyến BKM
\(\dfrac{AK}{NK}\cdot\dfrac{NB}{CB}\cdot\dfrac{CM}{AM}=1\\ \Rightarrow\dfrac{AK}{NK}\cdot\dfrac{1}{3}\cdot\dfrac{2}{3}=1\\ \Rightarrow\dfrac{AK}{NK}=\dfrac{9}{2}\)
Áp dụng Menelaus cho tam giác BMC và cát tuyến AKN
\(\dfrac{BK}{MK}\cdot\dfrac{MA}{CA}\cdot\dfrac{CN}{BN}=1\\ \Rightarrow\dfrac{KB}{KM}\cdot\dfrac{3}{2}\cdot\dfrac{1}{2}=1\\ \Rightarrow\dfrac{KB}{KM}=\dfrac{4}{3}\)
