This is the formula that when two terms squared are written with a minus sign between them their factors are the product of the original numbers once with a plus sign and once with the minus sign.
This can be explained by multiplying them.
(a-12b)
<u> *(a+12b) </u>
a²- 12ab
<u> +12ab - 144b² </u>
<u> a² +0 - 144b² </u>
We see we get the same answer as applying the formula above.