Anurag@Gurome wrote:Strongt wrote:is xy = -1?
1) x=y
2) y=1
(2)y = 1 implies x * (1) = -1, which implies x = -1. So xy = -1, which is again sufficient to answer the given question.
You're using the question here as though it were a fact. The question *asks* if xy = -1. We don't know if that's true, so we can't use it to draw any conclusions. Of course, if we assume that xy = -1 is true, then obviously we'll find out that xy = -1 is true - that's the "begging the question" fallacy in logic.
When we look at Statement 2 here, we have exactly one fact that we can use: y = 1. Since we know nothing else, we have no idea if xy = -1 is true. If x = -1, then indeed xy = -1. If x is anything else, then xy will not equal -1. So Statement 2 is not sufficient.
Statement 1 is sufficient, since if x = y, the answer to the question must be 'no'. But if you did try to consider both Statements together, the Statements here are in no way contradictory. Using both Statements, we know that x and y are both equal to 1. There's no contradiction there.
