hinh bn tu ve nhe
\(\infty:\)dong dang
\(\Delta ABD\infty\Delta ACE\)(g.g) \(\Rightarrow\frac{AE}{AD}=\frac{AC}{AB}\)
\(\Rightarrow AE.AB=AD.AC\) (1)
\(\Delta AMB\infty\Delta AEM\)(g.g) \(\Rightarrow\frac{AM}{AE}=\frac{AB}{AM}\Rightarrow AM^2=AE.AB\)(2)
\(\Delta ANC\infty\Delta ADN\)(g.g) \(\Rightarrow\frac{AN}{AD}=\frac{AC}{AN}\Rightarrow AN^2=AD.AC\)(3)
Tu (1), (2), (3) \(\Rightarrow AM^2=AN^2\Rightarrow AM=AN\)
\(\Rightarrow\)\(\Delta AMN\)can tai A