gmat prep data sufficiency

Think the answer is C

My approach was as under:

The problem states that (-a,b)(-b,a) are in the same xy plane. This can be true only when in cases where

- Both a and b have a positive value or
- Both a and b have a negative value

(given that ab is not equal to zero)

With this information we can use (2) which says ax>0. This means that x retains the sign of a. If a is a positive value, then x is positive and if a is negative, x is negative to make ax>0.

Now (1) tells us that xy>0 and hence y retains the sign of x.

Hence for any set of values for a and b (fulfilling the above 2 conditions)
(-x,y) would be in the same quadrant as (-a,b)(-b,a).

Prasanna wrote:Think the answer is C

My approach was as under:

The problem states that (-a,b)(-b,a) are in the same xy plane. This can be true only when in cases where

- Both a and b have a positive value or
- Both a and b have a negative value

(given that ab is not equal to zero)

With this information we can use (2) which says ax>0. This means that x retains the sign of a. If a is a positive value, then x is positive and if a is negative, x is negative to make ax>0.

Now (1) tells us that xy>0 and hence y retains the sign of x.

Hence for any set of values for a and b (fulfilling the above 2 conditions)
(-x,y) would be in the same quadrant as (-a,b)(-b,a).

excellent attempt ... me to getting the answer as C ...