The reason is because .
This one can be found on Wikipedia if my memory is correct. It is indeed a division by zero.
Indeed. I had a high school teacher. I was interested in his knowledge. I asked him something a bit advanced (modular arithmetic). He looked at me, blinked, and told me to finish my worksheet. Lame. I don't recall having any math teacher that actually was interested in maths.high school teachers are mostly idiots who only know what the school expects them to teach.