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Is 3x^2 - 2 > 0?

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Intern
Joined: 29 Nov 2015
Posts: 11
Is 3x^2 - 2 > 0?  [#permalink]

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13 Jan 2016, 22:35
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Difficulty:

25% (medium)

Question Stats:

77% (01:20) correct 23% (01:11) wrong based on 110 sessions

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Is 3x^2 - 2 > 0?

(1) x < 4
(2) x > -3
Math Expert
Joined: 02 Aug 2009
Posts: 7035
Re: Is 3x^2 - 2 > 0?  [#permalink]

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13 Jan 2016, 23:16
fattty wrote:
Is 3x^2 - 2 > 0?

(1) x < 4
(2) x > -3

Hi,
as usual , lets see the inequality and get some info out of it..
$$3x^2 - 2 > 0$$..
or $$x^2>\frac{2}{3}$$..
Now this to be true, x can not lie between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$

Lets see the statements now..
(1) x < 4
this range includes both x in between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$ and x outside it... insuff

(2) x > -3
again this range includes both x in between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$ and x outside it... insuff

combined.. the above point still remains.. insuff

E
_________________

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 3x^2 - 2 > 0?  [#permalink]

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17 Jan 2016, 03:10
chetan2u wrote:
fattty wrote:
Is 3x^2 - 2 > 0?

(1) x < 4
(2) x > -3

Hi,
as usual , lets see the inequality and get some info out of it..
$$3x^2 - 2 > 0$$..
or $$x^2>\frac{2}{3}$$..
Now this to be true, x can not lie between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$

Lets see the statements now..
(1) x < 4
this range includes both x in between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$ and x outside it... insuff

(2) x > -3
again this range includes both x in between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$ and x outside it... insuff

combined.. the above point still remains.. insuff

E

hi! I've just put 2 conditions -

Statement 1 - x < 4

x could = -1 and answer would be yes
or
x = 0 and answer is no

These numbers work for statement 2 as well, thus E.

Is that logic right?
Math Expert
Joined: 02 Aug 2009
Posts: 7035
Re: Is 3x^2 - 2 > 0?  [#permalink]

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17 Jan 2016, 03:15
lpetroski wrote:
chetan2u wrote:
fattty wrote:
Is 3x^2 - 2 > 0?

(1) x < 4
(2) x > -3

Hi,
as usual , lets see the inequality and get some info out of it..
$$3x^2 - 2 > 0$$..
or $$x^2>\frac{2}{3}$$..
Now this to be true, x can not lie between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$

Lets see the statements now..
(1) x < 4
this range includes both x in between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$ and x outside it... insuff

(2) x > -3
again this range includes both x in between $$\sqrt{\frac{2}{3}}$$ and $$-\sqrt{\frac{2}{3}}$$ and x outside it... insuff

combined.. the above point still remains.. insuff

E

hi! I've just put 2 conditions -

Statement 1 - x < 4

x could = -1 and answer would be yes
or
x = 0 and answer is no

These numbers work for statement 2 as well, thus E.

Is that logic right?

Hi,
you are correct..
if you pick up two numbers in the range , each giving different answers yes and no....
the outcome will be that the statement is not 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 3x^2 - 2 > 0?  [#permalink]

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31 Oct 2017, 04:34
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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Is 3x^2 - 2 > 0? &nbs [#permalink] 31 Oct 2017, 04:34
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