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Re: If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
Expert Reply
puneetfitness wrote:


karishma great that was very helpful one last question what if inequality was
x(x - 3) > 0 instead of
x(x - 3) < 0

Will it still hold true


Then look for the regions with the positive sign on your number line.

The solution will be x < 0 or x > 3
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Re: If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
boomtangboy wrote:
If x ≠ 0, is |x| < 1 ?

Whether this can be deduced\(-1<x<1\)

(1) \(x^2 < 1\)

\(-1<x< 1\)

Answer to the Question is YES, hence, sufficient

(2) \(|x| < \frac{1}{x}\)

\(\frac{-1}{x}<x<\frac{1}{x}\)

This is only possible for

\(0<x< 1\)

Answer to the Question is YES, hence, sufficient

Therefore, Opt (D)
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Re: If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
shikhar wrote:
My answer was A...
Explanation->
|x|<1 means x should be between -1 and 1.

from (1)
x2-1<0 => x between -1 and 1. sufficient

from (2)
if x +ve then same as 1 and sufficient
if x -ve then |x|=-x
-x2<1 or x2 > -1 not sufficient

so and A

Please correct me if wrong

Shikhar you have to check two sides of the absolute value. If you solve that equation in case
x>0 solution will be (0,1) interval
second case
x<0 solution is (-1,0) interval
combo is what we need
(-1,0) v (0,1)

Posted from my mobile device
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Re: If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
KarishmaB wrote:
Shef08 wrote:
This is what I did for statement 2:

|x|<1/x
As |x| will always be non negative, so the equation becomes:
X<1/x
Multiplying both sides by x
X^2<1
X^2-1<0 which is then to be worked out as the same way for st 1.

Experts please let me know is this method correct? Bunuel chetan2u VeritasKarishma
Please help

Posted from my mobile device


If we write |x| < 1/x as x < 1/x, then we are assuming that x is positive because |x| = x only when x >= 0.

x < 1/x
I cannot multiply both sides by x without knowing the sign of x. Here x could be positive or negative e.g.
when x = 1/2, x < 1/x
when x = -2, x < 1/x

So I won't multiply both sides by x. I take 1/x to the other side.

x - 1/x < 0

(x^2 - 1)/x < 0

So 0 < x < 1 or x < -1
But x must be positive so only 0 < x < 1 satisfies.

Now try putting |x| = -x when x is negative.



Hi KarishmaB great explanation.
One question here
(x^2 - 1)/x < 0
x^2 < 1
x<+-1
x< 1 or x < -1

Therefore not sure how is this become -1< x < 1 ?
Could you help clarify? Thanks
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If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
Bunuel wrote:
boomtangboy wrote:
If x≠0, is |x| <1?
(1) x2<1
(2) |x| < 1/x


If \(x\neq{0}\), is \(|x| <1\)?

    Is \(|x| <1\)?

    Is -\(1<x<1\) ? (\(x\neq{0}\))


(1) \(x^2<1\) --> \(-1<x<1\). Sufficient.

(2) \(|x| < \frac{1}{x}\)

Since LHS (|x|) is an absolute value, which is always non-negative, then RHS (1/x), must be positive (as \(|x| < \frac{1}{x}\)), so \(\frac{1}{x}>0\) --> \(x>0\).

Now, if \(x>0\) then \(|x|=x\) and we have: \(x<\frac{1}{x}\) --> since \(x>0\) then we can safely multiply both parts by it: \(x^2<1\) --> \(-1<x<1\), but as \(x>0\), the final range is \(0<x<1\). Sufficient.

Answer D.


Hi Bunuel, LHS (|x|) is an absolute value therefore x could be both positive and negative. So not sure why you mean |x| is always non-negative here?
RHS (1/x), if x is -2, then |x| < 1/x mean -2 < -1/2. Therefore x could be negative here.
Not sure where's my thinking going wrong? Could you help clarify? Thanks
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Re: If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
Expert Reply
Kimberly77 wrote:
KarishmaB wrote:
Shef08 wrote:
This is what I did for statement 2:

|x|<1/x
As |x| will always be non negative, so the equation becomes:
X<1/x
Multiplying both sides by x
X^2<1
X^2-1<0 which is then to be worked out as the same way for st 1.

Experts please let me know is this method correct? Bunuel chetan2u VeritasKarishma
Please help

Posted from my mobile device


If we write |x| < 1/x as x < 1/x, then we are assuming that x is positive because |x| = x only when x >= 0.

x < 1/x
I cannot multiply both sides by x without knowing the sign of x. Here x could be positive or negative e.g.
when x = 1/2, x < 1/x
when x = -2, x < 1/x

So I won't multiply both sides by x. I take 1/x to the other side.

x - 1/x < 0

(x^2 - 1)/x < 0

So 0 < x < 1 or x < -1
But x must be positive so only 0 < x < 1 satisfies.

Now try putting |x| = -x when x is negative.



Hi KarishmaB great explanation.
One question here
(x^2 - 1)/x < 0
x^2 < 1
x<+-1
x< 1 or x < -1

Therefore not sure how is this become -1< x < 1 ?
Could you help clarify? Thanks


When we have inequalities with linear factors, we plot them on the number line (search for wavy curve method) to get our range of interest.

(x^2 - 1)/x = (x + 1)(x - 1)/x

So plot -1, 0 and 1 on the number line. Since we want the negative regions, 0 < x < 1 and x < -1
Since x must be positive, the acceptable range is only 0 < x < 1

I will put up a YouTube video on this concept soon.
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Re: If x 0, is |x| < 1 ? (1) x^2 < 1 (2) |x| < 1/x [#permalink]
Thanks @KarishmaB...still not quite sure about the negative regions and and x must be positive here...
Looking forward to your YouTube video and thanks a bunch :please: :)
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