find pivot positions and columns

📌 What the video covers
- **Pivot positions**: Explains how to identify pivot positions in a matrix when performing row reduction.
- **Pivot columns**: Shows how pivot positions determine which columns are pivot columns.
- **Step‑by‑step demonstration**: Walks through examples of matrices, applying row operations to highlight pivots.
- **Connection to echelon form**: Links the idea of pivots to the process of putting a matrix into echelon or reduced echelon form.
- **Applications**: Notes how pivot columns are used in solving systems of linear equations and determining matrix rank.