Construim [tex]MN \perp BC[/tex].
Folosind proportii derivate din [tex] \frac{BD}{DC} = \frac{3}{4} => \frac{BD}{BC} =\frac{3}{4+3} =\frac{3}{7} [/tex].
[tex] \frac{A_{BMD}}{A_{ABC}} = \frac{MN \cdot BD/2}{AD \cdot BC/2} = \frac{MN \cdot BD}{2MN \cdot BC} =\\
= \frac{1}{2} \cdot \frac{BD}{BC}= \frac{1}{2} \cdot \frac{3}{7} = \frac{3}{14}
[/tex]
