Solution
= Solution
The two equal legs meet at the <right angle>, so the <Pythagorean theorem> gives $AB^2+AC^2=BC^2=4$, with $AB=AC$. Thus $AC=\sqrt2$. The midpoint condition then yields
$$
\boxed{AD=\frac{AC}{2}=\frac1{\sqrt2}\text{ units}.}
$$
= Solution
The two equal legs meet at the <right angle>, so the <Pythagorean theorem> gives $AB^2+AC^2=BC^2=4$, with $AB=AC$. Thus $AC=\sqrt2$. The midpoint condition then yields
$$
\boxed{AD=\frac{AC}{2}=\frac1{\sqrt2}\text{ units}.}
$$