Find all School-related info fast with the new School-Specific MBA Forum

It is currently 21 Oct 2014, 12:27

Close

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
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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If a and n are positive numbers, does 2a^{2x}=n?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
2 KUDOS received
Current Student
User avatar
Joined: 27 Jun 2012
Posts: 418
Concentration: Strategy, Finance
Followers: 44

Kudos [?]: 368 [2] , given: 182

If a and n are positive numbers, does 2a^{2x}=n? [#permalink] New post 03 Mar 2013, 14:44
2
This post received
KUDOS
00:00
A
B
C
D
E

Difficulty:

  85% (hard)

Question Stats:

44% (02:54) correct 56% (01:39) wrong based on 94 sessions
If a and n are positive numbers, does 2a^{2x}=n?

(1) a^x+\frac{1}{a^x}=\sqrt{n+2}

(2) x > 0
[Reveal] Spoiler: OA

_________________

Thanks,
PraPon

Tough 700+ Level RCs: Passage1 | Passage2 | Passage3 | Passage4 | Passage5 | Passage6 | Passage7
Reading Comprehension notes: Click here
VOTE: vote-best-gmat-practice-tests-excluding-gmatprep-144859.html
PowerScore CR Bible - Official Guide 13 Questions Set Mapped: Click here

1 KUDOS received
Senior Manager
Senior Manager
User avatar
Status: Final Lap
Joined: 25 Oct 2012
Posts: 294
Concentration: General Management, Entrepreneurship
GPA: 3.54
WE: Project Management (Retail Banking)
Followers: 2

Kudos [?]: 104 [1] , given: 85

Re: If a and n are positive numbers, does 2a^{2x}=n? [#permalink] New post 03 Mar 2013, 15:22
1
This post received
KUDOS
PraPon wrote:
If a and n are positive numbers, does 2a^{2x}=n?

(1) a^x+\frac{1}{a^x}=\sqrt{n+2}

(2) x > 0


(1) a^x+\frac{1}{a^x}=\sqrt{n+2} ALONE when squarred : ( a^{x} + a^{-x} )^2 = n+2

so, n = (a^{x} + a^{-x})^{2} - 2

n = a^{2x}+a^{-2x}+2a^{x}*a^{-x}-2 (a^{x}*a^{-x}=1)

n = a^{2x}+a^{-2x}

back to the question :

2a^{2x}-n = 2a^{2x}-a^{2x}-a^{-2x}
2a^{2x}-n = a^{2x}-a^{-2x}

Hence, A insufficent

(2) x > 0 ALONE

Clearly insufficent

both (1) and (2) INSUFF

Thus, Answer is E ..
_________________

KUDOS is the good manner to help the entire community.

"If you don't change your life, your life will change you"

Expert Post
4 KUDOS received
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 10 Oct 2012
Posts: 627
Followers: 43

Kudos [?]: 597 [4] , given: 135

Premium Member
Re: If a and n are positive numbers, does 2a^{2x}=n? [#permalink] New post 03 Mar 2013, 21:53
4
This post received
KUDOS
Expert's post
PraPon wrote:
If a and n are positive numbers, does 2a^{2x}=n?

(1) a^x+\frac{1}{a^x}=\sqrt{n+2}

(2) x > 0


We know that (a^x+a^-x)^2 = a^2x+a^-2x+2.

From F.S 1, we have (n+2) =a^2x+a^-2x+2

or n =a^2x+a^-2x. Thus, the question stem is asking whether 2a^2x= n?

If it has to be true, then a^2x+a^-2x = 2a^2x.

or a^(4x) = 1. Now, for x=0, we get a YES. But depending on the values of a and x, this will change. Thus, insufficient.

From F.S 2, we only have x>0. Clearly Insufficient.

Combining both, we know that x is not equal to zero. However, if a=1, we can still get a^4x = 1. Insufficient.

E.
_________________

All that is equal and not-Deep Dive In-equality

Hit and Trial for Integral Solutions

1 KUDOS received
CEO
CEO
User avatar
Joined: 09 Sep 2013
Posts: 2804
Followers: 206

Kudos [?]: 42 [1] , given: 0

Premium Member
Re: If a and n are positive numbers, does 2a^{2x}=n? [#permalink] New post 12 May 2014, 21:12
1
This post received
KUDOS
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Re: If a and n are positive numbers, does 2a^{2x}=n?   [#permalink] 12 May 2014, 21:12
    Similar topics Author Replies Last post
Similar
Topics:
2 Experts publish their posts in the topic If n and y are positive integers and n represents the number WishMasterUA 6 22 Aug 2011, 05:34
1 Experts publish their posts in the topic Does the prime number p divide n!? surendar26 4 20 Dec 2010, 09:10
If a and n are positive, does 2a^(2x) = n? seofah 3 14 Apr 2007, 13:56
For all positive integers n, /n/ is defined as the number kevincan 7 16 Nov 2006, 07:33
If a and n are positive integers, does 2a^(2x) = n condition mrmikec 9 11 Jun 2006, 19:03
Display posts from previous: Sort by

If a and n are positive numbers, does 2a^{2x}=n?

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.