Our math instructor went to a conference and left a quiz for our substitute teacher to administer. The problem we had to solve, using the law of cosines was “What are the angles of this 5, 2, 1 triangle?” The other students were struggling to apply the formula (which gave strange numbers), but I had forgotten the formula. I started to derive the formula when I recognized that the base was too big for the short sides. I was the only one that got the right answer: “This is not a triangle.” The instructor apologized the next week for the mistake.
Our computer science lecture hall had a large green motorized chalkboard that the lecturer could raise while filling the board. Our instructor drew the flowchart for a sort program, filling the board. When he was done, he turned to the class, all proud of himself. I called out, “That won’t work!” He said, “Who said that?” I replied, “I did.” Then I explained that every time around the loop he was setting his continue flag, when it should be reset at the start of the loop, and be set whenever an item was found to be out of order, and had been swapped to get closer to its correct position. When a pass finished without swapping any items, then the sort was complete. His code would loop forever. He said, “Oh, that’s a detail.” I replied with the same inflection, “Oh, that’s programming.” The hall erupted with applause.
Once in a later lab, he wrote Pi on the white board to 20 decimal places. Once again, he turned to the class, all pleased with himself. I called out, “There is a mistake.” He said, “Who said that?” I replied, “I did.” He asked, “Where is it wrong?” I said, “Just a minute.” I started tapping on my table with my fingers. He said, “Whoa, I got to see this!” He must have thought I was using chisanbop, the Korean way of calculating similar to an abacus, using just fingers. I told him what the error was, and he asked how I did that. I told him I know a poem in which the letter count in each word is a digit of Pi:
Sir, I bear a rhyme excelling
in mystic force and magic spelling.
Celestial sprites elucidate,
all my own striving can’t relate.”
3.14159265358979323846
I was just counting the letters using my fingers.
The next two digits happen to be 26, the first pair of digits to repeat.