Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 350,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Re: DS: A positive [#permalink]
18 Oct 2008, 22:20

rishi2377 wrote:

Is A positive? 1. x^2-2*x+A is positive for all x 2. A*x^2+1 is positive for all x

The questioin is not clear !!!

1) is insufficient since x(x-2)>-A With different x A changes

if we say CASE1 1. x^2-2*x+A is positive for all x INSUFFI 2. A*(x^2)+1 is positive for all x SUFFI different result !!! else if we say CASE 2 1. x^2-2*x+A is positive for all x INSUFFI 2. (A*x)^2+1 is positive for all x INSUFFI different result !!!

in second case CASE2 above ,(2) is INSUFFI since A can be +ve or -ve

In case1 ,(2) is SUFFI ,A needs to be +ve -ve value cannot suffice !! _________________

Re: DS: A positive [#permalink]
21 Oct 2008, 05:09

GMAT TIGER wrote:

rishi2377 wrote:

Is A positive?

1. x^2-2*x+A is positive for all x 2. A*x^2+1 is positive for all x

Remember for all x!!!

In statement 1, can anybody prove that A is -ve if 0 < x < 2?

Therefore A.

Hi, why are you limiting to 0<x<2?

My solution. 1) simplifies to A>x(2-x). A is +ve for any value 0<x<2; and could be +ve or -ve for all other values. Insufficient. 2) simplifies to A > -1/(x^2); A can be +ve or -ve for any value of x (except for x=0); therefore Insufficient. 1 and 2 together also insufficient, e.g. at x=3, (1) gives A>-3 and (2) gives A>-1/9; therefore A could still be either -ve or +ve; Answer E

PS I'm not sure if this helps visualize, as I don't know how to explain it ... I see (1) as an parabola cutting x axis at 0 and 2, center at 1,1; and (2) as a kind of hyperbola below the x axis.

Re: DS: A positive [#permalink]
21 Oct 2008, 06:44

Every one who are sticking with E is missing my point. Try to understand what exactly meant by "for all x ". You never agree with me on OA (as A) if you keep on missing this statement: "for all x ".

If A is +ve, that value works for all x. If A is -ve, that value doesnot work for all x.

Re: DS: A positive [#permalink]
21 Oct 2008, 06:55

Some examples will help.

Thanks GMAT Tiger

GMAT TIGER wrote:

Every one who are sticking with E is missing my point. Try to understand what exactly meant by "for all x ". You never agree with me on OA (as A) if you keep on missing this statement: "for all x ".

If A is +ve, that value works for all x. If A is -ve, that value doesnot work for all x.

Re: DS: A positive [#permalink]
21 Oct 2008, 07:25

bigfernhead wrote:

Some examples will help.

Thanks GMAT Tiger

GMAT TIGER wrote:

Every one who are sticking with E is missing my point. Try to understand what exactly meant by "for all x ". You never agree with me on OA (as A) if you keep on missing this statement: "for all x ".

If A is +ve, that value works for all x. If A is -ve, that value doesnot work for all x.

Therefore A must be +ve.

If any, will clearify again.

from statement 1:

(x^2 - 2x + A) > 0 (x^2 - 2x +1) + (A -1) > 0 (x-1)^2 + (A -1) > 0

suppose if x = 1, the inequality becomes: (A -1) > 0. so A has to be >1 to satisfy the inequality. Therefore A must be +ve.

The easiest way to understand this problem is that "when 1 > x > -1, A must be positive; when x>1 but <-1, A can either be positive or negative. Therefore the value of A has to be +ve for all values of x. Hence A is positive

Hello everyone! Researching, networking, and understanding the “feel” for a school are all part of the essential journey to a top MBA. Wouldn’t it be great... ...

Are you interested in applying to business school? If you are seeking advice about the admissions process, such as how to select your targeted schools, then send your questions...