Answer: To show his father what he had done
Step-by-step explanation:
Percy Jackson is the son of the great Greek god of the seas, Poseidon. He did not however, know this for a long time. After he finds out, his life becomes more exciting as he embarks on many adventures.
According to Grover who is his best friend and guardian, Percy sent Medusa's head to Mount Olympus to show his father what he had done so that Poseidon would acknowledge and be proud of him.