Factoring negative quantity from algebraic expression?

[Holocene]

Factoring negative quantity from algebraic expression?

Why is this wrong?

$$\displaystyle{28xy^2 - 14x = -14x(-2y^2 + 1)}$$

The book instead does this:

$$\displaystyle{28xy^2 - 14x = -7x(-4y^2 + 2)}$$

 

[flebbyman]

Your book is incorrect

 

[Hurkyl]

Those are both valid factorizations.