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If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 <

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If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 00:17
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If x is negative, is x <-3?

(1) x^2 > 9
(2) x^3 < -9


OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/if-x-is-negat ... 07229.html
[Reveal] Spoiler: OA

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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 00:44
IEsailor wrote:
If x is negative, is x <-3?
(1) x^2 > 9
(2) x^3 < -9


(1) x^2>9
|x|>3
x>3 OR x<-3.
Not Sufficient.

(2) x^3<-9
The greatest value of x can be between -2 and -3.
-2^3=-8
-3^3=-27

So, x is definitely less than -2 but we don't know whether it is less than -3.
Not Sufficient.

Combining both we know x<-3.
Ans: "C"
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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 00:52
a gives |x| > 3 meaning regions x<-3 and x>3. not sufficient.

b gives x < 0. x < =-3 and -2<x<=-3. not sufficient.

a+b

region x<-3 is the answer.

C
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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 05:30
(1)
(x-3)(x+3) > 0

x < -3 or x > 3

(2)
x^3 < -9

x is -ve, but if x = -2.5

(-2.5)^3 < -9, but x > -3

(1) + (2)

x < -3

Answer - C
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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 08:09
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1)
\(x<-3\) and \(x>3\),
we are given that \(x<0\), so only \(x<-3\) holds true, sufficient

2)
\(x<-2.2\) (it's estimation of \(\sqrt[3]{9})\), not sufficient.

(A)

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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 08:38
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ulm wrote:
1)
\(x<-3\) and \(x>3\),
we are given that \(x<0\), so only \(x<-3\) holds true, sufficient

2)
\(x<-2.2\) (it's estimation of \(\sqrt[3]{9})\), not sufficient.

(A)


True!!! Thanks!!!
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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 12:28
I also missed that x is negative in the question steam. Thanks for pointing out.

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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 13:16
from stmnt (2) x.x.x<-9
if x=-3 , x.x.x=-27 ,-27<-9 , -3>-3 the answer is no
if x=-4 ,x.x.x=-64, -64<-9 , -4>-3 the answer is no
by taking different values we can conclude that x is not greater than -3.

by taking x=-2, x.x.x=-8, -8 is not less than -9 ,which makes statement (2) false.

Then answer is (d)

Is my above reasoning correct. plz explain

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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 13:40
TomB wrote:
from stmnt (2) x.x.x<-9
if x=-3 , x.x.x=-27 ,-27<-9 , -3>-3 the answer is no
if x=-4 ,x.x.x=-64, -64<-9 , -4>-3 the answer is no
by taking different values we can conclude that x is not greater than -3.

by taking x=-2, x.x.x=-8, -8 is not less than -9 ,which makes statement (2) false.

Then answer is (d)

Is my above reasoning correct. plz explain


What if x=-2.5. Nowhere it's mentioned that x must be an integer.
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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 19 May 2011, 15:40
Good point there @ulm.

1. Sufficient

as x<-3

2. Not sufficient

x^3<9

=> x may or may not be less than -3.

Answer is A.

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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 < [#permalink]

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New post 29 Nov 2017, 00:47
If x is negative, is x < –3 ?

(1) x^2 > 9 --> \(x<-3\) or \(x>3\) as given that \(x<0\) then we have that \(x<-3\). Sufficient.

(2) x^3 < –9 --> if \(x=-3\) (\(x^3=-27<-9\)) then the answer will be NO (as \(x\) equals to -3 and is not less than -3) but if \(x=-4\) (\(x^3=-64<-9\)) then the answer will be YES. Not sufficient.

Answer: A.

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Re: If x is negative, is x <-3? (1) x^2 > 9 (2) x^3 <   [#permalink] 29 Nov 2017, 00:47
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