Expression $\displaystyle 28xy^2-14x$

my solution = $\displaystyle 14x(2y^2-1)$ or could also be $\displaystyle -14x(-2y^2+1)$

The book lists the solution as $\displaystyle -7x(-4y^2+2) $, are they both correct? And how do I know what to factor out to get consistent numbers with the book? In general I always factor out the largest possible number, in this case 14.