1. Let's clarify the notation: QM, PQ, MQ, and QP represent distances or vectors between points Q, M, and P. 2. The order matters because distance or vector from point A to B is generally different from B to A in vector terms (direction matters). 3. If calculating distances (lengths), $QM$ and $MQ$ are equal because distance is symmetric: $QM = MQ$. 4. However, if calculating vectors, $\overrightarrow{QM} = -\overrightarrow{MQ}$, so direction changes. 5. Similarly, $PQ$ and $QP$ differ in direction but have the same length. 6. We calculate $QM$ and $PQ$ (not $MQ$ and $QP$) because the problem or method likely defines the direction from Q to M and from P to Q. 7. This choice ensures consistency in vector operations like addition or subtraction. 8. In summary, the choice depends on the problem's context and direction conventions.