Why is (n-1)(n+1)=n^2-1?
Last Updated: 29.06.2025 02:12

The more direct answer is to look at a rectangle with sides of n + 1 and n - 1, let’s go with n = 2
xxxx
xx
The Day the Earth Smiled: Earth, the Moon, and Saturn All in One Frame - The Daily Galaxy
So, that’s a rectangle with sides 2 and 4.
n^2 - 1
The basic answer is that you cross-multiply the values in each factor:
Hometown hero: Suárez soaks up the spotlight in Mexico City - NASCAR.com
xxx x
Move the nub up to the top:
If you cut off the end of that rectangle, you make it smaller, 2 * 3 and a separate nub of size 1 * 2
The AI-generated ad that aired during the NBA finals took $2,000 and 2 days to make - Mashable
xxxx
(n - 1)(n + 1)
xxx
xxx
n^2 - n + n - 1
And you are left with almost a square. One less than the square of side n.
Super-magnetic dead star throws a violent temper tantrum as NASA X-ray spacecraft looks on - Space
xxx x