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If x = 3y, is x^2 > y^2? [#permalink]
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08 Oct 2006, 23:14
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If x = 3y, is x^2 > y^2? (1) y+x < yx (2) x^2 = 9y^2
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Senior Manager
Joined: 16 Sep 2006
Posts: 406

x=3y
Stat1 : x+y<x*y
4y<3y^2
4<3y
4<x
x>4
therfore x is Positive and >4
Therefore x^2>y^2
Stat2 : is neway given in the question itself
Statement 1 is enough in itself to arrive at the anwser.
choice A
Not sure if this is the rite way to do it. It's just an attempt



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Joined: 01 May 2006
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(D) for me.
No need statments
x = 3*y
=> x^2 = 9*y^2 Thus, x^2 > y^2



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iced_tea wrote: Fig wrote: (D) for me. No need statments x = 3*y => x^2 = 9*y^2 Thus, x^2 > y^2 what if y = 0 ?
Yes :D ... U are right .... always this case of y=0 or x=0, the one to keep in mind
Thus, it turns to be (A)



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Re: DS  x, y [#permalink]
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09 Oct 2006, 08:22
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if x^2>y^2
implies 9y^2>y^2
implies 8y^2>0 whic is always true for all values of y except zero.
so whichever option can let me know that either x or y are not zero.i'm through.
1. x+y<y*x
so 4y<3y^2
so y(y4/3)<0
solving which we get either y>4/3 or <zero.
hence y cant be zero.hence x cant be zero.
so this choice helpsme ensure that y ,x cant assume zero value.
2. in this x=y=0 is a posiblity.
hence choice A should be the answer.
iced_tea wrote: If x=3y, is x^2>y^2?
1). y+x<y*x
2). x^2=9y^2



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Re: If x=3y, is x^2>y^2? 1). y+x<y*x 2). x^2=9y^2 [#permalink]
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27 Feb 2014, 09:56
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Re: If x = 3y, is x^2 > y^2? [#permalink]
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25 Mar 2014, 21:31
iced_tea wrote: If x = 3y, is x^2 > y^2?
(1) y+x < yx
(2) x^2 = 9y^2 1) As x=3y > 4y<3y^2 > y>(4/3) and x > 4 Number sub. If y=5/3 > x=5 > x^2>y^2 If y=2 > x=6 > x^2>y^2 So, 1 alone is sufficient. 2) x = 3y > x^2=9y^2. So, not sufficient. Therefore, A is the answer



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Re: If x = 3y, is x^2 > y^2? [#permalink]
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25 Mar 2014, 23:28
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iced_tea wrote: If x = 3y, is x^2 > y^2?
(1) y+x < yx (2) x^2 = 9y^2 Sol: Subsitute for x and we need to know whether 8y^2> 0 Or whether y is equal to zero or not From st 1 we see that 4y<3y^2 or y*(3y4) >0 We see that either y>0 and y>4/3 or y<0 or y< 4/3 This implies y not equal to zero hence thenl statement is suff. St2 is same info as given in the question stem So and is A Posted from my mobile device
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Re: If x = 3y, is x^2 > y^2? [#permalink]
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25 May 2015, 13:29
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Re: If x = 3y, is x^2 > y^2? [#permalink]
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30 Jul 2015, 07:54
Question after re arranging becomes is (x+y)(xy)>0.
So your question becomes is x>y>o?
1) subbing x=3y you know that y>0 and consequently x>0 therefore sufficient.
2) tells you nothing but repeats the stem therefore insufficient.
A
Cheers!
G



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Re: If x = 3y, is x^2 > y^2? [#permalink]
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13 Aug 2016, 09:24
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Re: If x = 3y, is x^2 > y^2?
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