1/ $NM⊥AB$ và $AC⊥AB$
$→\dfrac{MN}{AC}=\dfrac{BM}{BA}=\dfrac{BN}{BC}$ (ĐL Talet)
$→\dfrac{MN}{9}=\dfrac{1}{4}=\dfrac{BN}{15}$
$→\begin{cases}MN=2,25\\BN=3,75\end{cases}$
$→A$
2/ $DE//BC$
$→\dfrac{AD}{AB}=\dfrac{x}{BC}$ (ĐL Talet)
$→0,4=\dfrac{x}{6,5}$
$→2,6=x$
$→D$