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Is X^2=?X?? (1)X^2+X>0 (2)X<1, My

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Is X^2=?X?? (1)X^2+X>0 (2)X<1, My [#permalink] New post 15 Dec 2007, 22:21
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Is X^2=│X│?

(1)X^2+X>0

(2)X<1,

My answer is ,

first, X^2=│X│ can be reformed │X│^2=│X│
│X│^2-│X│=0
│X│(│X│-1)=0, X=0, +1, -1


(1)
X(X+1)>0
X<-1 , 0<X
, when X=-1 No, X=0 No, X=1 Yes
so, A can not be possible

(2) X<1,
, when X=-1 Yes, X=0 yes, X=1 No
so, B can not be possible

(1)+(2) is,
X<-1 , 0<X<1
, when X=-1 No, X=0 No, X=1 No

I think the answer is C(coz, this is Data sufficiency Question, No can be answer)

However, some say it is E

I am not confident with my answer,

Am I terribly wrong?

P.S: I am so sorry to make you confused, I rewrited, check this again PLS.

Last edited by leokkim on 16 Dec 2007, 03:24, edited 4 times in total.
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 [#permalink] New post 16 Dec 2007, 08:32
C

Is X^2=│X| at X e {-1,0,+1}

(1)X^2+X>0 ==> X e (-∞,-1)&(0,+∞). includes {1}. INSUFF.

(2)X<1 ==> X e (-∞,1). includes {-1,0} INSUFF.

(1)&(2) ==> X e (-∞,-1)&(0,1). does not include numbers of set {-1,0,+1} SUFF.
  [#permalink] 16 Dec 2007, 08:32
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