Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

X = ?

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 472
Joined: Sun Mar 29, 2009 6:54 pm
Thanked: 56 times

by ssmiles08 » Thu Jun 11, 2009 4:43 pm
square both sides: 8xy - 16y^2 = x^2

so x^2 - 8xy + 16y^2 = 0

(x-4y)(x-4y) = 0

x = 4y.

(D)
Top
Join the discussion
Legendary Member
Posts: 752
Joined: Sun May 17, 2009 11:04 pm
Location: Tokyo
Thanked: 81 times
GMAT Score:680

by tohellandback » Thu Jun 11, 2009 5:42 pm
I don't understand this..whats wrong with the following

x = sqrt(8xy-16y^2)
we know that x=0
putting x=0 and squaring both sides
16y^=0
y=0

so it can be any of the options.

where did you get the question from?
The powers of two are bloody impolite!!
Top
Join the discussion
User avatar
Master | Next Rank: 500 Posts
Posts: 472
Joined: Sun Mar 29, 2009 6:54 pm
Thanked: 56 times

by ssmiles08 » Thu Jun 11, 2009 5:52 pm
tohellandback wrote: we know that x=0
silly me...I always seem to rush pass the questions. you are right. y = 0. Something with the question is wrongly worded. Are you sure it said x =0? or maybe it said x =/= 0 instead?
Top
Join the discussion
Legendary Member
Posts: 594
Joined: Thu Aug 14, 2008 11:51 pm
Thanked: 12 times

by nervesofsteel » Thu Jun 11, 2009 10:36 pm
This question is from GMAt sets...

I don't if this question is wrongly worded...
Top
Join the discussion
Legendary Member
Posts: 594
Joined: Thu Aug 14, 2008 11:51 pm
Thanked: 12 times

by nervesofsteel » Thu Jun 11, 2009 10:39 pm
ssmiles08 wrote:square both sides: 8xy - 16y^2 = x^2

so x^2 - 8xy + 16y^2 = 0

(x-4y)(x-4y) = 0

x = 4y.

(D)

I think this is the right approach...
Top
Join the discussion
Legendary Member
Posts: 752
Joined: Sun May 17, 2009 11:04 pm
Location: Tokyo
Thanked: 81 times
GMAT Score:680

by tohellandback » Thu Jun 11, 2009 10:53 pm
nervesofsteel wrote:
ssmiles08 wrote:square both sides: 8xy - 16y^2 = x^2

so x^2 - 8xy + 16y^2 = 0

(x-4y)(x-4y) = 0

x = 4y.

(D)

I think this is the right approach...
My goal here is not to match the OA because I am sure this exact question is not going to be there on the test.
now even if you agree to
x=4y, or y=x/4
since x=0, y=0.
or, x=– 4y
or x=4y
or x=y
or x=4y
or x=4y^2
so where is this wrong
The powers of two are bloody impolite!!
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 119
Joined: Tue Jan 20, 2009 10:16 pm
Thanked: 9 times
GMAT Score:730

by mikeCoolBoy » Fri Jun 12, 2009 12:08 am
since x = 0 and x = sqrt(8xy-16y^2)

substituting x = 0 ---> 0 = sqrt(-16y^2) that I believe can only be true if y = 0 making C the correct answer.

So I agree with ssmiles08 and tohellandback that something is wrong with the question.
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 103
Joined: Fri May 22, 2009 3:56 am
Thanked: 4 times
GMAT Score:470

by gmatplayer » Fri Jun 12, 2009 6:47 am
if x=0=y
then all answer choices are correct. This can't be GMAT problem.
Top
Join the discussion
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Sat Jun 27, 2009 1:36 am

by jerrykid » Mon Aug 31, 2009 7:06 pm
I think that x=0 only would make all choices correct.

But if x=0 AND x=(8xy-16y^2)^(1/2), then y=0 and x=4y. Therefore, D should be the answer.
Beat the GMAT !!!
Top
Join the discussion