Alec was looking at a pattern of square numbers when he discovered a math trick.

He wanted to figure out how this trick worked, so he used deductive reasoning to make the argument below:

1. Let n = any number

2. Observation: $\displaystyle{\left({n}+{1}\right)}\cdot{\left({n}-{1}\right)}={{n}}^{{2}}-{1}\usepackage{cmbright}\Huge\$

3. $\displaystyle{\left({n}+{1}\right)}\cdot{\left({n}-{1}\right)}={{n}}^{{2}}-{n}+{n}-{1}={{n}}^{{2}}-{1}\usepackage{cmbright}\Huge\$

According to his argument above, which of the following tricks did he discover?