Answer:
Using definition of midpoint, Q is the mid point of PR.
Step-by-step explanation:
Given 2PQ=PR
And Q lies on the line PR (It should be given in the problem itself else we have to assume it to prove "Q is the midpoint of PR").
Then PR=PQ+QR using segment addition postulate.
Let us plugin PR in given equation.
2PQ=PQ+QR
Subtract PQ from both sides.
2PQ-PQ=PQ+QR-PQ
PQ=QR
Since Q lies on the line PR and PQ=QR, Q is the mid point of PR.
Hence proved.
