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If x is an integer, is x|x|<2^x ?

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If x is an integer, is x|x|<2^x ? [#permalink] New post 18 Dec 2012, 07:31
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If x is an integer, is x|x|<2^x ?

(1) x < 0
(2) x = -10
[Reveal] Spoiler: OA
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Re: If x is an integer, is x|x|<2^x ? [#permalink] New post 18 Dec 2012, 07:35
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Walkabout wrote:
If x is an integer, is x|x|<2^x ?

(1) x < 0
(2) x= -10


If x is an integer, is x|x|<2^x ?

Notice that the RHS (right hand side) of the expression is always positive (\(2^x>0\)), but the LHS is positive when \(x>0\) (\(x>0\) --> \(x*|x|=x^2\)), negative when \(x<0\) (\(x<0\) --> \(x*|x|=-x^2\)) and equals to zero when \(x={0}\).

(1) x < 0. According to the above \(x*|x|<0<2^x\). Sufficient.

(2) x = -10. The same here \(x*|x|=-100<0<\frac{1}{2^{10}}\). Sufficient.

Answer: D.
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DS from OG [#permalink] New post 30 Dec 2013, 10:42
If x is an integer, is x |x| < 2^x ?

(1) x < 0
(2) x = –10

DS from OG.
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Last edited by seabhi on 31 Dec 2013, 01:45, edited 1 time in total.
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Re: DS from OG [#permalink] New post 30 Dec 2013, 11:02
seabhi wrote:
If x is an integer, is x |x| < 2x ?

(1) x < 0
(2) x = –10

DS from OG.


OA is D for the following reasons:
When you first see a DS question, see if there is anyway to simplify the question stem
In this case, since |x| is positive, we can divide both sides by |x| giving us a new question stem --> is x < 2?

S1: x<0, therefore x must be <2 = sufficient
S2: x = -10 and -10 < 2 = sufficient

Let me know if this helps!
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Re: DS from OG [#permalink] New post 30 Dec 2013, 20:36
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bparrish89 wrote:
seabhi wrote:
If x is an integer, is x |x| < 2x ?

(1) x < 0
(2) x = –10

DS from OG.


OA is D for the following reasons:
When you first see a DS question, see if there is anyway to simplify the question stem
In this case, since |x| is positive, we can divide both sides by |x| giving us a new question stem --> is x < 2?

S1: x<0, therefore x must be <2 = sufficient
S2: x = -10 and -10 < 2 = sufficient

Let me know if this helps!



The OA is wrong here because of the following reasons:


(1) if x=-10 then -100<-20, on the other hand if x= -1, x<0 then the inequality changes from < to >, namely, -1 > -2 ; This statement is absolutely insufficient!


(2) This statement is obviously sufficient!


So, the correct answer is notD, but B
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Re: DS from OG [#permalink] New post 31 Dec 2013, 01:46
Apologies for the confusion, the Question has been corrected.
It was not 2x but 2^x
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Re: DS from OG [#permalink] New post 31 Dec 2013, 03:07
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If x is an integer, is x|x|<2^x ? [#permalink] New post 27 Jul 2015, 05:40
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If x is an integer, is x|x|<2^x ?

(1) x < 0
(2) x = -10
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If x is an integer, is x|x|<2^x ? [#permalink] New post 27 Jul 2015, 05:43
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reza52520 wrote:
If x is an integer, is x|x|<2^x ?

(1) x < 0
(2) x = -10


Question : Is x|x|<2^x ?

Statement 1: x < 0

For x to be Negative LHS i.e. x|x| will always be NEGATIVE
and 2^x will be positive for any value of x
i.e. x|x|<2^x will always be true
SUFFICIENT

Statement 1: x = -10
For x =-10 LHS i.e. x|x| will always be NEGATIVE (-100)
and 2^x will be positive for given x (1/2^10)
i.e. x|x|<2^x will always be true
SUFFICIENT

Answer: option D
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Last edited by GMATinsight on 27 Jul 2015, 05:44, edited 1 time in total.
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Re: If x is an integer, is x|x|<2^x ? [#permalink] New post 27 Jul 2015, 05:44
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reza52520 wrote:
If x is an integer, is x|x|<2^x ?

(1) x < 0
(2) x = -10


Hi,
we have an equation and the RHS 2^x will be positive irrespective of value of x and LHS xlxl will depend on the value of x..
1) x is -ive .. so LHS is -ive and RHS is +ive.. suff
2) x=-10... again LHS is -ive and RHS is +ive.. suff
ans D
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Re: If x is an integer, is x|x|<2^x ? [#permalink] New post 13 Dec 2015, 10:47
For,
and 2^x will be positive for any value of x

2 power x, X can be negative no?
since its x, we dont know positive or negative..
What am I missing?
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Re: If x is an integer, is x|x|<2^x ? [#permalink] New post 13 Dec 2015, 11:04
paidlukkha wrote:
For,
and 2^x will be positive for any value of x

2 power x, X can be negative no?
since its x, we dont know positive or negative..
What am I missing?


You are missing a crucial thing here. Even if x is <0, \(2^x\) with x<0 = \(1/2^x\) , it is still >0...(1)

Thus with x<0, |x| = -x and hence x|x| = -\(x^2\)

As, x^2 is always \(\geq\) 0 for all x, -\(x^2\)<0 ...(2)

Thus, from (1) and (2), you get a definite "yes" for the question "is \(x|x| < 2^x\)" for x<0.

Hope this helps.
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Re: If x is an integer, is x|x|<2^x ?   [#permalink] 13 Dec 2015, 11:04
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