If two lines intersect prove that the vertically opposite angles are equal

Explanation

To prove that vertically opposite angles are equal when two lines intersect, let's follow these steps:

### Step-by-Step Solution:

1. **Identify the Lines and Angles**:
- Let the two intersecting lines be \( AB \) and \( CD \), intersecting at point \( O \).
- The angles formed at the intersection are \( \angle 1 \), \( \angle 2 \), \( \angle 3 \), and \( \angle 4 \). Here, \( \angle 1 \) and \( \angle 2 \) are vertically opposite angles, as well as \( \angle 3 \) and \( \angle 4 \).

...