If `A(2, 3, 4), B(5, 4, -1), C(3, 6, 2)` and `D(1, 2, 0)` be four points, show that `vec(AB)` is perpendicular to `vec(CD)`.

Explanation

To show that the vector \( \vec{AB} \) is perpendicular to the vector \( \vec{CD} \), we need to calculate both vectors and then find their dot product. If the dot product is zero, then the vectors are perpendicular.

### Step 1: Find the coordinates of vectors \( \vec{AB} \) and \( \vec{CD} \)

1. **Calculate \( \vec{AB} \)**:
\[ \vec{AB} = \vec{B} - \vec{A} \]
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