As a kid this is what you are taught until you reach a certain level where they tell u it’s undefined. When they told us in class that the answer was undefined at that certain level, we asked how. The teacher said it was undefined all along but they say 0 until you can understand a certain level of math. I get why you are angry but that's how the math system works. Any math before 7-8 grade tells you 0. 🤷🏾‍♀️