Once there was a verbal fight between an engineer , a mathematician and a physicist.
A guy with school bag on his back approach them and ask them that the person who can draw the largest amount of area using the least amount of fence will be the winner.

All of them accept the challenge.

The engineer guy made the fence in a big circle and said it the best.

The physicist made a long line and said that the length was infinite. Then he said that fencing half of the Earth was the best.

The mathematician smiled and so something which made him clear winner.
What did he do?