thevinh, you are absoluteley right. You can lose info by taking square root.

(x+2)^2<1 is unambiguous.

(x+2+1)(x+2-1)<0->

-3<x<-1, which is what you did.

However, back to OP. Plato is right, taking square roots can lead to ambiguities (and loss of solutions as thevinh points out)

So either

1) a^2>0 -> a='0, or

2) a^2>0 -> a>0, or

3) a^2>0 -> lal>0 -> a>0 or a<0.

The only thing pointing to 2) or 3) is that they lead to quadratic inequalities, the title of the OP.