VeritasPrepKarishma wrote:

Archit143 wrote:

Need Help!!! Urgent

What is the difference between the solution of below problems, Is there any difference in the approach:-

1. X^3 > X

soln: -1<X<0 or X>1

If we follow the above principle for solving than the answer to below equation must be:

2. a^3< a^2 + 2a

-1<a<0 or a>2

but the answer as per MGMAt quant book is

0<a<2 or a<-1

Pls help me in getting the right concept.........

Responding to a pm:

2. a^3< a^2 + 2a

a^3 - a^2 - 2a < 0

a(a - 2)(a + 1) < 0

......-1.....0............2.......

Since you want the expression to be negative, the required range is a < -1 or 0 < a < 2 (Notice the sign in the original inequality. It is less than)

The range you have written: -1<a<0 or a>2 is for the expression to be positive.

Check out these posts for further clarification:

http://www.veritasprep.com/blog/2012/06 ... e-factors/http://www.veritasprep.com/blog/2012/07 ... ns-part-i/http://www.veritasprep.com/blog/2012/07 ... s-part-ii/http://www.veritasprep.com/blog/2012/07 ... qualities/Karishma

You are no less than Ron ...I would rate you above them in Maths

I mean what great explanations.......

can you fw the links of your blog on MODULUS, various type of questions.....

Thanks a trillion....I am sure i have added atleast 1 point to my maths score.......

Was it so simple!!!!!!!!I am thinking now!!!!!!!!!!!!!!!!!!!!

Waiting for links on modulus!!!!!!!!!!!!!

Archit