[填空题]
Two points A and B have coordinates (2,3,1) and ()8vg -udeyp qz55-ekss 6u3 le5,9,3)4mfa0*jlqj myb1e3 :0) zy1hiz; joia respectively.
1. 1. Find $\overrightarrow{\mathrm{AB}}$.
2. Find $|\overrightarrow{\mathrm{AB}}|$ .
Let $\overrightarrow{\mathrm{AC}}=4 \mathbf{i}+2 \mathbf{j}-4 \mathbf{k}$ .
2. Find the angle between $\overrightarrow{\mathrm{AB}} $ and $ \overrightarrow{\mathrm{AC}}$. ≈
3. Find the area of triangle A B C .≈
4. Hence, or otherwise, find the shortest distance from C to the line passing through A and B .≈
