Factorise completely $125p^3 - 5p$.

First take out the common factor $5p$: $125p^3 - 5p = 5p(25p^2 - 1)$. The bracket is a difference of two squares, $25p^2 - 1 = (5p)^2 - 1^2$, so it factorises further into $(5p - 1)(5p + 1)$. The complete factorisation is $5p(5p - 1)(5p + 1)$.