solving the two sides : xy+z = xy+xz =>z=xz=>z(x-1)=0=> z=0 or x-1=0=>x=1

Hi Maihuna,

thanks for the answer.

It's logical...sometime I makes things more difficult then they are...

One more point on this one - keep in mind that with a "MUST BE TRUE" question, an answer choice with "and" is significantly harder than an answer choice with "or". "And" means that both conditions MUST BE met, whereas "or" means that one or the other will do.

On this one, they use A as a trap answer because if z = 0, then it doesn't matter what x is, the equation is satisfied. So, mentally, you're looking at z = 0 and saying "yes, that satisfies the equation if x also = 0", but that doesn't HAVE TO BE the case; that's just one situation in which the equation works.

So with that MUST BE TRUE standard, make sure you pay particular attention to that kind of wording like "and" vs. "or". "And" means that two independent things must both be true, and that's a pretty high burden of proof...

Hi Brian,

thanks for the advice. Its like you said..I haven't seen a question like this before, checked A and said...well looks right for me