Gmat Prep 2 ques x-y plane

[abhinav85]

If ab is not equal to 0 and points (-a,b) and (-b,a) are in the same quardant of the xy - plane. Is point (-x,y) in this same quardant?

A) xy>0

B) ax>0.

[spoiler]C[spoiler][/spoiler]

[tohellandback]

Answer C:
Reason:
if (-a,b) and (-b,a) are in the same quadrant, they must have the same sign. This satisfies two quadrants
quadrant 2 and 4
1) insufficient because (-x,y) can be in any of these two quadrants.
2) still the same condition-Insufficient
combine 1 and 2
let's say a,b are negative.
using 2- x has to be negative and so does y-
(-a,b)-4th quadrant
(-x,y) 4th quadrant
if a,b are positive
x and y have to be positive and so
(-a,b) in 2nd quadrant
(-x,y) in 2nd quadrant

Hope it helps.

Plz let me know if explanation is not clear

[abhinav85]

Hey tohellandback
how you got this: i mean why these 2 quardants??


"if (-a,b) and (-b,a) are in the same quadrant, they must have the same sign. This satisfies two quadrants
quadrant 2 and 4"


Thanks

[tohellandback]

lt's say a and b are both negative -5 and -3 resp
(-a,b)=5,-3
(-b,a)=3,-5 both in 4th quadrant

now consider both positive 5 and 3 resp
(-a,b)=-5,3
(-b,a)=-3,5
both 2nd quadrant
consider one negative and other positive 5 and -3 resp
(-a,b)=-5,-3 third quad
(-b,a)=3,-5 4th quadrant so they are in different quadrant

Hope it helps