Solution:
In the given figure, we can see, $\mathrm{LM} \| \mathrm{CB}$,
By using basic proportionality theorem, we get, $\mathrm{AM} / \mathrm{AB}=\mathrm{AL} / \mathrm{A} \mathrm{C} \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots(\mathrm{i})$
Similarly, given, $\mathrm{LN} \| \mathrm{CD}$ and using basic proportionality theorem, $\therefore \mathrm{AN} / \mathrm{AD}=\mathrm{AL} / \mathrm{AC} \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots(\mathrm{ii})$
From equation (i) and (ii), we get,
$\mathrm{AM} / \mathrm{AB}=\mathrm{AN} / \mathrm{AD}$
Hence, proved.