Answer
$$2$$
Work Step by Step
$$\vec{AB}= \lt 0,1 \gt -\lt 1,0 \gt =\lt -1, 1 \gt \\ \vec{AC}=\lt 0,-1 \gt -\lt 1,0 \gt =\lt -1, -1 \gt$$
Now, $\vec{AB}\times\vec{AC}=\begin{vmatrix}\hat{i}&\hat{j}&\hat{k}\\-1&0&0\\-1&-1&0\end{vmatrix}= 2\hat{k}$
and $|\vec{AB}\times\vec{AC}|=\sqrt {(2)^2}=\sqrt 4 =2$
