Math Files@Math_files
A mathematics professor once discovered that the sink in his kitchen had broken. He called a plumber, who arrived the next day, tightened a few fittings, and quickly fixed the problem.
The professor was pleased—until he saw the bill.
“This is a third of my monthly salary!” he exclaimed.
Still, he paid it. As the plumber was leaving, he said, “I understand your situation. Why not join our company? You could earn much more than you do now. Just one thing—when you apply, say you only finished elementary school. They prefer that.”
The professor, intrigued, followed the advice. To his surprise, he was hired. The work was simple—occasional repairs, tightening pipes—and his income improved dramatically.
Some time later, the company introduced a new rule: all employees had to attend evening classes to complete basic schooling. The professor had no choice but to attend.
On the first day, the subject was mathematics. The instructor asked a student to write the formula for the area of a circle on the board. The professor was chosen.
He walked up confidently—but then hesitated. He couldn’t recall the formula.
Determined, he began deriving it from scratch. The board quickly filled with integrals, derivatives, and complex expressions. After several minutes of work, he arrived at a result:
−πr²
Unsatisfied with the negative sign, he tried again. And again. Each time, the same result appeared.
Frustrated, he turned to the class. Behind him, the other plumbers were whispering to one another:
“Switch the limits of the integral.”
