Why is (n-1)(n+1)=n^2-1?
15.06.2025 02:52

n^2 - n + n - 1
(n - 1)(n + 1)
xxx x
What can you do if you are a full-grown adult, but never experienced being a child?
So, that’s a rectangle with sides 2 and 4.
xx
xxxx
xxx x
n^2 - 1
If you cut off the end of that rectangle, you make it smaller, 2 * 3 and a separate nub of size 1 * 2
At what stage in your life did you realize, "No, I can't do this any more" and walk out? Why?
The more direct answer is to look at a rectangle with sides of n + 1 and n - 1, let’s go with n = 2
xxx
xxxx
Move the nub up to the top:
The basic answer is that you cross-multiply the values in each factor:
xxx
And you are left with almost a square. One less than the square of side n.