Where does this relation come from? $n^2-1 \approx (n-1)2$ for $n-1 \ll 1$ I came across the relation in the title in a physics textbook and wondered how I get to it.
$$n^2-1 \approx (n-1)2$$
for $$n-1\ll 1$$
Could anybody maybe help me out?
Thanks!

$n^2-1=(n+1)(n-1)$ so if $n$ is very close to $1$, then $n+1$ is very close to $2$ and $n^2-1$ is very close to $2(n-1)$.
