Mathematics

The key insight is the midsegment theorem: when you connect the midpoints of two sides of a triangle, you create a segment that's parallel to the third side and exactly half its length. Since $S$ and $T$ are midpoints of $PQ$ and $PR$, the segment $ST$ forms a midsegment opposite to $QR$—so you just need to find half the length of $QR$.

The key insight is the midsegment theorem: when you connect the midpoints of two sides of a triangle, you create a segment that's parallel to the third side and exactly half its length. Since $S$ and $T$ are midpoints of $PQ$ and $PR$, the segment $ST$ forms a midsegment opposite to $QR$—so you just need to find half the length of $QR$.