Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 23 May 2017, 09:15

GMAT Club Daily Prep

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

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

How many intersects with x-axis

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
Intern
Joined: 20 Aug 2010
Posts: 38
Followers: 1

Kudos [?]: 25 [0], given: 0

How many intersects with x-axis [#permalink]

Show Tags

26 Nov 2011, 12:54
00:00

Difficulty:

(N/A)

Question Stats:

100% (00:00) correct 0% (00:00) wrong based on 6 sessions

HideShow timer Statistics

How many intersects with x-axis does y=x^2+2qx+r have

I) q^2>r

II) r^2>q
Intern
Joined: 11 Nov 2011
Posts: 14
Followers: 0

Kudos [?]: 26 [0], given: 4

Re: How many intersects with x-axis [#permalink]

Show Tags

26 Nov 2011, 19:22
I think it is A.

The question can be rephrased: when is x^2+2qx+r = 0

Using the quadratic formula we find that x = (-2q +/- sqrt(4q^2 - 4r)/2)

From this we can see that there will be two solutions if 4q^2 - 4r > 0, one solution if 4q^2 - 4r = 0 and zero solutions if 4q^2 - 4r < 0.

From the information in 1.:
If q^2 > r then 4q^2 - 4r > 0.

SUFFICIENT - there are two points of intersection on the y axis.

From the information in 2.:
If r^2>q we don't know if 4q^2 - 4r is positive. We try two cases to demonstrate this:
if q = 1 and r = -2 then r^2>q and 4q^2 - 4r > 0
if q = 1 and r = 2 then r^2>q but 4q^2 - 4r < 0

This information is INSUFFICIENT.

So I chose A.
Re: How many intersects with x-axis   [#permalink] 26 Nov 2011, 19:22
Display posts from previous: Sort by

How many intersects with x-axis

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.