Why is (n-1)(n+1)=n^2-1?
10.06.2025 16:10

xx
xxx x
xxx
The basic answer is that you cross-multiply the values in each factor:
n^2 - n + n - 1
If you cut off the end of that rectangle, you make it smaller, 2 * 3 and a separate nub of size 1 * 2
The Best Tech Gifts for Father’s Day 2025 - Gizmodo
The more direct answer is to look at a rectangle with sides of n + 1 and n - 1, let’s go with n = 2
n^2 - 1
(n - 1)(n + 1)
xxx
And you are left with almost a square. One less than the square of side n.
xxx x
xxxx
xxxx
Move the nub up to the top:
Has anyone ever really waited that long and gotten a paper check mailed 20 days ago?
So, that’s a rectangle with sides 2 and 4.