I tired searching this on the internet and could not find an answer.

Why is it that when you take any number and square it and then take the numbers one higher than that number and one lower than that number and then multiple them, they will always be one less than the number you get when you square it?

Example One :

1 x 1 = 1

0 x 2 = 0

Example Two :

-5 x -5 = 25

-4 x -6 = 24

Just so you know I am horrible at math and have not tested this with too many numbers and do not really know if it works with all numbers or just many numbers or just the ones I tested. Also I tend to flip the mess out of everything in my head. I also do not know if this is already widely known or anything and if it is I would like to know the name of it.