Question

How do you factor `3p^2 q^2-12n^2`?

Answer 1

Extract the obvious common factor
`3p^2q^2-12n^2`
`=3(p^2q^2 - 4n^2)`

Not that the second factor is the difference of squares with a common factoring:
`=3((pq)^2-(2n)^2)`
`=3(pq-2n)(pq+2n)`