He was refusing to deviate from the answers provided by the course material. This happened to me so many times in high school. I remember in another biology class, a different teacher insisted that the probability of rolling five dice and having all the dice be the same was 1 in 7,776. I argued for at least 15 minutes in front of the entire class that it wasn't and I wasn't going to drop it. The teacher left the room and got the answer key from the text book to show me how wrong I was. Since reasoning wasn't working, I went home and simulated 100,000 similar dice rolls on my Commodore 64 to show that the odds were indeed 1 in 1,296.

After that, he capitulated and asked me to write a proof and send it to the textbook publisher.