Inequalities

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Inequalities

by Troika » Sat Oct 27, 2012 7:06 pm
Is x^3 > x^2?

1. X > 0

2. X^2 > X

OA : C

Source: MGMAT Equations, 4th ed., pg. 187

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by anuprajan5 » Sat Oct 27, 2012 10:02 pm
Hi Troika,

The answer is C

Statement 1 - X>0

Since the question does not mention as to whether x is an integer, we could take fractions into the fray as well. We know that positive integers raised to a higher power will be greater than to the same integer raised to a lower power. But that does not hold for fractions. Examples:

2^3>2^2
But (1/2)^3<(1/2)^2

Insufficient

Statement 2 - x^2>x

This can hold for both negative and positive integers. But in the case of negative integers, this will not hold for the question.

2^2>2 and 2^3>2^2
(-2)^2>-2 but -2^3<-2^2


[spoiler]Combined, we know that the number is positive and that x^2>x^3. This holds true only for positive integers. Hence C[/spoiler]
Regards
Anup

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