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Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1

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Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 10 Sep 2018, 17:53
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Question Stats:

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Is x > 0?


(1) (x^2 - 1)(x^3) > 0

(2) x^2 < 1
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Joined: 02 Aug 2009
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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 10 Sep 2018, 18:14
jennysussna wrote:
Is x>0?

1. (X^2 - 1) (x^3) > 0
2. X^2 < 1

Posted from my mobile device


1) \((x^2-1)(x^3)>0\)
If x>0.....x^3>0 and x^2-1>0 or x^2>1...X>1
If x<0...x^3<0 and x^2-1<0 or x^2<1.... So x>-1
Both cases possible
Insufficient

2) x^2<1
-1<X<1
Insufficient

Combined
If x>0, x>1 but statement II says otherwise it says X is <1, so X can not be greater than 0
So x<0
Sufficient

C
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 10 Sep 2018, 18:35
chetan2u wrote:
jennysussna wrote:
Is x>0?

1. (X^2 - 1) (x^3) > 0
2. X^2 < 1

Posted from my mobile device


1) \((x^2-1)(x^3)>0\)
If x>0.....x^3>0 and x^2-1>0 or x^2<1...0<X<1
If x<0...x^3<0 and x^2-1<0 or x^2>1.... So x<-1
Both cases possible
Insufficient

2) x^2<1
-1<X<1
Insufficient

Combined
If x <0, X<-1 but statement II says otherwise..
So x>0


For statement one I combined to have X^5-X^3>0 as I thought that was easier to test than solve out the inequality.

Can you clarify on the last part? What do you mean statement II means otherwise? How do you go from having 0<X<1 and x<-1 from the first statement and then -1<X<1 from the second to having combined 'If x <0, X<-1'? I am still confused how this makes x>0?

I tested -(1/2) and it was true for both statements, so it seems that x is negative.
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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 10 Sep 2018, 18:57
jennysussna wrote:
chetan2u wrote:
jennysussna wrote:
Is x>0?

1. (X^2 - 1) (x^3) > 0
2. X^2 < 1

Posted from my mobile device


1) \((x^2-1)(x^3)>0\)
If x>0.....x^3>0 and x^2-1>0 or x^2<1...0<X<1
If x<0...x^3<0 and x^2-1<0 or x^2>1.... So x<-1
Both cases possible
Insufficient

2) x^2<1
-1<X<1
Insufficient

Combined
If x <0, X<-1 but statement II says otherwise..
So x>0


For statement one I combined to have X^5-X^3>0 as I thought that was easier to test than solve out the inequality.

Can you clarify on the last part? What do you mean statement II means otherwise? How do you go from having 0<X<1 and x<-1 from the first statement and then -1<X<1 from the second to having combined 'If x <0, X<-1'? I am still confused how this makes x>0?

I tested -(1/2) and it was true for both statements, so it seems that x is negative.


Hi..
I wrote the opposite signs by mistake..
So (x^2-1)(x^3)>0...
So two case
1) both are positive
x^3>0, x^2>1..X>1
2) both negative
x^3<0, x^2<1...-1<X<0
Insufficient

But statement II says x^2<1..
Individually it is insufficient
But when you add it to the info of statement I..
x^2<1 means x^3 is also <0 or X<0
Sufficient
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 12 Sep 2018, 07:57
chetan2u

Just to be sure i fully understand it:

S(1) + S(2): results in the following range for x -->

-1<x<0



Which implies that x is not x>0, am I correct???
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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 12 Sep 2018, 08:06
1
T1101 wrote:
chetan2u

Just to be sure i fully understand it:

S(1) + S(2): results in the following range for x -->

-1<x<0



Which implies that x is not x>0, am I correct???



Yes combined it tells us -1<X<0
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 13 Sep 2018, 10:46
jennysussna wrote:
Is x > 0?


(1) (x^2 - 1)(x^3) > 0

(2) x^2 < 1


OA:C

\((1) \quad (x^2 - 1)(x^3) > 0\)

It leads to two cases
Case 1
\((x^2-1)>0\) AND \(x^3>0\)
This leads to \(x>1\)

OR

Case 2
\((x^2-1)<0\) AND \(x^3<0\)
This leads to \(-1<x<0\)

So \(x\) can be either \(x>1\) OR \(-1<x<0\)
Statement \(1\) alone is insufficient

\((2) \quad x^2 < 1\)
This leads to \(-1<x<1\)
Statement \(2\) alone is insufficient

Combining \((1)\) and \((2)\), we get \(-1<x<0\).
After combining \((1)\) and \((2)\), there is a definite answer to the question: Is x > 0? No
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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1  [#permalink]

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New post 14 Sep 2018, 08:31
This is a yes/no Q.

Start with statement 2 as it is easier to evaluate. According to statement 2 x could be a positive fraction such that x lies between 0 & 1 or a negative fraction which lies between -1 and 0. Clearly we have two answers (a Yes & a No) to the same questions hence statement 2 alone is not sufficient to answer whether x>0? Strike out option B & D.

Statement 1 alone would give the same result as in statement 2; if x is a negative fraction which lies between -1 and 0 then we have a no but if x >1 then we have a yes. Hence insufficient.

Combining 1 and 2 we get only one answer that is x is a negative fraction which lies between -1 and 0. And we have a No to the Q. Ans C is correct.
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Re: Is x > 0? (1) (x^2 - 1)(x^3) > 0 (2) x^2 < 1 &nbs [#permalink] 14 Sep 2018, 08:31
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