### UC Berkeley Web Feature

Math expert fields questions big and small at Cal Day

BERKELEY – Professor George Bergman, the man behind the longstanding "Ask a Mathematician" table at Cal Day, doesn't appreciate comparisons with Lucy, the pseudo psychiatrist in the "Peanuts" comic strip.

"The theme of that (comic) is always how abrasive and unhelpful she is, and I think I am usually able to be helpful," said Bergman, the Cal Day mathematician - with almost all of the answers - since 1992. "I am very happy when I finish an explanation and the person I'm talking to says, 'That's cool!'"

Before his first "Ask a Mathematician" stint, Bergman said he "worried that I would be pelted with smart-aleck questions, but it's not been anything like that. The public has been very friendly."

Over the years, Bergman said, he's fielded Cal Day questions from very young children, high school and college students, and their parents. Typical mathematically unsophisticated queries, he said, range from "What's the idea of calculus?" to "Why isn't (the answer to) infinity divided by infinity just 1?"

One boy around the age of 5 asked him for the opposite of zero. "Well," Bergman responded, "opposite can mean different things." To illustrate that not everything has a well-defined opposite, the professor said he asked the child, "For instance, what's the opposite of you?" The boy pointed to his little sister.

Practical questions also abound, said Bergman.

For instance, someone needed to know the formula for the height of a regular tetrahedron in order to do a video simulation. They worked it out together on the spot, he said. Another Cal Day visitor inquired about a situation where a Petri dish is plated with two strains of bacteria, and a colony forms whenever a bacterium of one strain is within a critical distance of a bacterium of another strain. After much discussion, Bergman suggested that a statistician probably would be of more help than a mathematician.

He admitted that he occasionally is asked questions he can't answer, at least not right away. Like the time a high school student asked how to evaluate the integral corresponding to the calculation of the length of a segment of a sine curve. Bergman took the youth's address, looked up the information later, and mailed it to him.

And one year, the mathematics chair at Head-Royce School in Oakland said one of his students had produced his own proof of the Pythagorean theorem. He wondered if it was correct and if it was something new. Bergman referred the question to colleague Robin Hartshorne, a professor with an interest in the history of mathematics. Hartshorne looked at the student's proof, compared it to others, and concluded that it seemed to be new and should be published, with some clarifications.

Inevitably, there are non-mathematical questions that come Bergman's way. The most common is from parents asking what math course their child should start with at UC Berkeley. Other frequent questions include directions to the restroom and to other Cal Day activities.

As for directions to the "Ask a Mathematician" table, look for Bergman on the west side of Evans Hall.