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Is x^2 > 15? (1) x > -4 (2) x^3 < 0

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Is x^2 > 15? (1) x > -4 (2) x^3 < 0 [#permalink] New post 22 May 2012, 13:51
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  5% (low)

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56% (01:43) correct 44% (00:15) wrong based on 16 sessions
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Re: Is x^2 > 15? (1) x > -4 (2) x^3 < 0 [#permalink] New post 22 May 2012, 14:04
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Is x^2 > 15?

Is x^2>15? --> is x<-\sqrt{15} or is x>\sqrt{15}?

(1) x > -4 --> if -4<x<-\sqrt{15} or if x>\sqrt{15} then the answer is YES but if -\sqrt{15}\leq{x}\leq{\sqrt{15}} then the answer is NO. Not sufficient.

(2) x^3 < 0 --> x<0 --> if x<-\sqrt{15} then the answer is YES but if -\sqrt{15}\leq{x}<0 then the answer is NO. Not sufficient.

(1)+(2) x>-4 and x<0 --> -4<x<0 --> if -4<x<-\sqrt{15} then the answer is YES but if -\sqrt{15}\leq{x}<0 then the answer is NO. Not sufficient.

Answer: E.

Hope it's clear.
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Re: Is x^2 > 15? (1) x > -4 (2) x^3 < 0 [#permalink] New post 22 May 2012, 14:41
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maybe is a bit comfortable to work with number on a number line instead of \sqrt{15} (is the same after all)

1) x > - 4 -----> -3,9 is largest than 15 but -3 NO but again +5 yes insuff

2) x^3 < 0 ---> x is negative -----> -1 is NO -5 is YES Insuff

1) + 2) we have only negative value but -1 is YES -3.9 is NO -----> E

Thanks Bunuel .
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Re: Is x^2 > 15? (1) x > -4 (2) x^3 < 0   [#permalink] 22 May 2012, 14:41
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