A young man in an advanced math lecture fell asleep in class. The professor meanwhile wrote two problems on the blackboard as illustrations of equations that had no solution. He explained their history and discussed some of the great minds that had been up against them only to fail time and again. When the bell rang, the young man awoke, looked at the blackboard and, thinking the two equations were his homework, he copied them down and ran to his next class.
The following Monday, the young man came to class and told his professor that his homework was the toughest assignment he'd ever had. He wasn't sure about the second one, but he'd gotten the first. Sure enough, he had solved one of the "impossible" problems, because he didn't know it was impossible.