Inequality

[gmattesttaker2]

Hello,

I came across this Data Sufficiency problem that was posted here sometime ago:

Is a > 0?

1. a^3 - a < 0
2. 1 - a^2 > 0


The OA is C

My approach is as follows:

1) a^3 - a < 0

=> a^3 < a

If a = -2 then, -8 < -2 - True
If a = 1 then, 1 < 1 - False

In-sufficient

2) 1 - a^2 > 0

=> (1+a)(1-a) > 0
(1+a) > 0 and (1-a) > 0
or
(1+a) < 0 and (1-a) < 0

=> a > -1 and a < 1
or a < -1 and 1 < a

=> 1 > a > -1
or 1 < a < -1

In-sufficient

I am not sure how to proceed further from this point onwards by combining both. Can you please assist? Thanks a lot.

Best Regards,
Sri

[Anurag@Gurome]

Refer to the post here >> https://www.beatthegmat.com/a-challengin ... tml#480245

...
=> a > -1 and a < 1
or a < -1 and 1 < a...

Do not blindly follow logic. Always cross check it's feasibility.
If a is less than -1, it cannot be greater than 1.

[gmattesttaker2]

Refer to the post here >> https://www.beatthegmat.com/a-challengin ... tml#480245

...
=> a > -1 and a < 1
or a < -1 and 1 < a...

Do not blindly follow logic. Always cross check it's feasibility.
If a is less than -1, it cannot be greater than 1.

Hi Anurag,

Thanks for your reply. It is clear now.

Best Regards,
Sri