mikemcgarry wrote:

Given that xy > 0, which of the following must also be greater than zero?

(A)

x + y(B)

x^2 + y(C)

(x + y)^2(D)

x^2 - y^2 + 100(E)

(x - y)^2For a discussion of plugging in numbers, as well as a full solution to this question, see:

http://magoosh.com/gmat/2013/how-to-plu ... questions/Mike

Actually if u just go through the options.. you'll notice that option C, is a perfect square.. which has to be greater than or equal to zero. Now looking back at the question, we know xy>0, which implies x and y are not equal to 0 and are of same sign. therefore x+y will be a non zero number and its square would be greater than 0.

Ans C it is.

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