Data Sufficiency

gmattester wrote:If a^2 - b^2=0, does a=0
1) ab=0
2)b=-b

I think in some of the solutions above, people are not using the information provided in the question. We know, to begin with, that

a^2 - b^2 = 0

There are a few ways to rewrite this, but no matter how you do, you should find that

|a| = |b|

That is, if a is zero, then b must be zero, and vice versa.

From 1), we know either a is zero or b is zero, so the other must be zero as well. Sufficient.

Statement 2 could only be true if b is zero, so a must be zero as well. Sufficient.

D.