# $\Delta ABC$ is a right triangle,right-angled at A and $AD\perp BC$.Then $\large\frac{BD}{DC}$=____
$\begin{array}{1 1}\big(\large\frac{AB}{AC}\big)^2\\\big(\large\frac{AB}{AC}\big)\\\big(\large\frac{AB}{AD}\big)^2\\\big(\large\frac{AB}{AD}\big)\end{array}$