Evaluate: $(723)(723)-(722)(724)$.
To evaluate this expression, I notice that it has the form $(a)(a)-(a-1)(a+1)$ for some $a$. In this case, $a=723$, but I wonder if I can simplify the expression by using a more general identity for this form. I recall that $(a)(a)-(a-1)(a+1) = a^2 - (a^2-1) = 1$ for any $a$, since the terms $a^2$ cancel out. So, regardless of what $a$ is, the expression is always equal to $1$. This means that I don't have to do any tedious calculations with large numbers, and I can just write the answer as $1$. 