Question

Answer 1

Giải thích

*BM cắt DC tại F.

△ABM có: AB//DF \(\Rightarrow\dfrac{BM}{MF}=\dfrac{AM}{MD}=\dfrac{AM}{2AM}=\dfrac{1}{2}\) (định lí Ta-let)

△BCF có: \(\dfrac{BM}{MF}=\dfrac{BN}{NC}=\dfrac{1}{2}\Rightarrow\)MN//BC//AB (định lí Ta-let đảo).

△ADC có: ME//DC

 \(\Rightarrow\dfrac{ME}{DC}=\dfrac{AM}{AD}=\dfrac{AM}{AM+MD}=\dfrac{AM}{AM+2AM}=\dfrac{1}{3}\) (hq định lí Ta-let)

\(\Rightarrow ME=\dfrac{DC}{3}=\dfrac{3}{3}=1\left(cm\right)\)

Answer 2

Chọn B