A man buys an acre of land on which stands a huge oak tree. He hires a crew to remove the tree. After many hours, the foreman tells the man that the tree is attached to a huge block of oak and they must figure out what it is before they can remove the tree.
Months later, the man's accountant comes out to the site and tells the man that he is bankrupt.
The man says desperately, “But I must find out what that block of oak is!”
The accountant replies, “Don't you know?”
“It's a square root!”