Why is (n-1)(n+1)=n^2-1?
Last Updated: 29.06.2025 15:12

So, that’s a rectangle with sides 2 and 4.
n^2 - n + n - 1
xxx
xxxx
And you are left with almost a square. One less than the square of side n.
xxxx
(n - 1)(n + 1)
The basic answer is that you cross-multiply the values in each factor:
xxx
xxx x
The more direct answer is to look at a rectangle with sides of n + 1 and n - 1, let’s go with n = 2
xx
Vera Rubin quarter coin released by US Mint - BBC Sky at Night Magazine
n^2 - 1
xxx x
If you cut off the end of that rectangle, you make it smaller, 2 * 3 and a separate nub of size 1 * 2
Hell Is Us' Intriguingly Bold Design Decisions Refuse To Give You A Hint - GameSpot
Move the nub up to the top: