In $\triangle PQR$, if $PQ = PR$ and $D, E, F$ are midpoints of $QR, PR, PQ$ respectively, then $DE$ and $DF$ are—

Since $PQ = PR$, the triangle is isosceles. $DE$ and $DF$ are mid-segments parallel to and half of $PQ$ and $PR$ respectively; as $PQ = PR$, it follows that $DE = DF$.