why is x over zero is undefined?
You mean x/0, right?
The reason is related to the associated multiplication question.If you divide 6 by 3 the answer is 2 because 2 times 3 IS 6. If you divide 6 by zero, then you are asking the question, "What number times zero gives 6?" The answer to that one, of course, is no number, for we know that zero times any real number is zero not 6. So we say that division by zero is undefined, for it is not consistent with division by other numbers.
How many 2's are in 6? Well 2+2+2 = 6 so three 2's are in 6.
But how many 0's are in 6? Well 0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+ 0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+ 0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0
But that's not 6! That's still just 0... That means that there must be an infinite amount of 0's in a number, or even more than infinite
To keep it simple, we just say it's undefined.