Tricky DS, Inequality

[bretania]

Is X > Y?

1. X + Y > 0
2. X^2 > Y^2

[tytyros]

IMO A....questions asks whether X-Y > 0

1 is sufficient
2. is insufficient since x > y and x > -y when squared give the same result

[clock60]

Originally Posted by tytyros

IMO A....questions asks whether X-Y > 0

1 is sufficient
2. is insufficient since x > y and x > -y when squared give the same result

what about x=-3 y=7
-3+7=4>0 but x is not larger than y
or x=7 y=3 7+3=10 x>y
my vote for C
(2) (x-y)(x+y)>0
x-y>0 and
x>-y
st 1 directly says that x>-y so x>y
C

[llutsar]

Originally Posted by clock60

what about x=-3 y=7
-3+7=4>0 but x is not larger than y
or x=7 y=3 7+3=10 x>y
my vote for C
(2) (x-y)(x+y)>0
x-y>0 and
x>-y
st 1 directly says that x>-y so x>y
C

If x>-y, how can you conclude that also x>y, clock60? In my opinion both points are inconclusive an the answer is E.

[12rk34]

1. X + Y > 0
X > -Y, INSUFFICIENT
2. X² > Y²
X² - Y² > 0
(X+Y)(X-Y) > 0
Either X > -Y and X > Y
or X < -Y and X < Y
INSUFFICIENT
Combining the two,
(X+Y)(X-Y) > 0 from statement (1)
(X-Y) > 0 (since (X+Y) > 0 from statement (1) )
X > Y SUFFICIENT
Hence C.

[clock60]

Originally Posted by llutsar

If x>-y, how can you conclude that also x>y, clock60? In my opinion both points are inconclusive an the answer is E.

for (x-y)(x+y)>0 two conditions must be maintain
first is x-y>0
and second (x+y)>0
the product of two positive numbers is always positive from the first we are given that x>-y or x+y>0 hence x-y>0 so x>y

[Crack_Mat]

1. is not sufficient. as if x + y > 0 is does not give any hint that X > Y!!!!!
2. is needed and it says that x-y> 0 based on above point.

[Crack_Mat]

answer C, as both need to make the decision!

[sksgill]

Originally Posted by 12rk34

1. X + Y > 0
X > -Y, INSUFFICIENT
2. X² > Y²
X² - Y² > 0
(X+Y)(X-Y) > 0
Either X > -Y and X > Y
or X < -Y and X < Y
INSUFFICIENT
Combining the two,
(X+Y)(X-Y) > 0 from statement (1)
(X-Y) > 0 (since (X+Y) > 0 from statement (1) )
X > Y SUFFICIENT
Hence C.

great explanation thanks

[wanderwanderer]

answer is C.