Câu hỏi của Nguyễn Trí Thiện

a.Ta có:\(\dfrac{MD}{ED}=\dfrac{4}{12}=\dfrac{1}{3};\dfrac{ND}{FD}=\dfrac{5}{15}=\dfrac{1}{3}\)=> MN//EF ( Ta-lét đảo )b. ta có: MN//EF(cmt)\(\Rightarrow\dfrac{MN}{EF}=\dfrac{DM}{DE}=\dfrac{DN}{DF}\)\(\Leftrightarrow\dfrac{8}{EF}=\dfrac{1}{3}\)\(\Leftrightarrow EF=24cm\) Câu trả lời: a.Ta có:\(\dfrac{MD}{ED}=\dfrac{4}{12}=\dfrac{1}{3};\dfrac{ND}{FD}=\dfrac{5}{15}=\dfrac{1}{3}\)=> MN//EF ( Ta-lét đảo )b. ta có: MN//EF(cmt)\(\Rightarrow\dfrac{MN}{EF}=\dfrac{DM}{DE}=\dfrac{DN}{DF}\)\(\Leftrightarrow\dfrac{8}{EF}=\dfrac{1}{3}\)\(\Leftrightarrow EF=24cm\)