It is currently 23 Mar 2018, 00:22

### 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

# PS: x^2

Author Message
Senior Manager
Joined: 07 Jan 2008
Posts: 383

### Show Tags

20 Aug 2008, 00:23
00:00

Difficulty:

(N/A)

Question Stats:

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

### HideShow timer Statistics

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Director
Joined: 14 Aug 2007
Posts: 703

### Show Tags

20 Aug 2008, 00:32
$$x^2y^2+3xy-18=0$$
$$xy(xy+6)-3(xy+6) = 0$$
xy=3 or xy=-6

both positive so xy cant be -6

$$x^2y^2=9$$

$$x^2 = 9/y^2$$
Senior Manager
Joined: 29 Mar 2008
Posts: 345

### Show Tags

20 Aug 2008, 00:36

x^2y^2 =18-3xy

One other method is to substitute the answer choices.

Try the easier ones first. When x^2=9/(y^2) is substituted in the given equation, we get 9=9 and hence the answer choice D.
_________________

To find what you seek in the road of life, the best proverb of all is that which says:
"Leave no stone unturned."
-Edward Bulwer Lytton

Senior Manager
Joined: 16 Jul 2008
Posts: 285

### Show Tags

20 Aug 2008, 00:46
It seemed easier to solve the quadratic equation for xy. You get (xy-3)(xy+6)=0. Then xy = 3; -6. But both are positive so only one answer left.
_________________

http://applicant.wordpress.com/

Manager
Joined: 27 Mar 2008
Posts: 78

### Show Tags

20 Aug 2008, 15:17
Nerdboy wrote:
It seemed easier to solve the quadratic equation for xy. You get (xy-3)(xy+6)=0. Then xy = 3; -6. But both are positive so only one answer left.

Agree quadratic is faster than plugging in.

x & y = positive is key to answering 9/y^2

D
Manager
Joined: 30 Jul 2007
Posts: 130

### Show Tags

21 Aug 2008, 12:50
Why not E? that would work as well.
Manager
Joined: 27 Mar 2008
Posts: 78

### Show Tags

21 Aug 2008, 12:55
sarzan wrote:
Why not E? that would work as well.

x,y must be positive. -6^2 yields 36 but cannot use b/c does not follow rules
Manager
Joined: 30 Jul 2007
Posts: 130

### Show Tags

21 Aug 2008, 12:56
As mentioned before, the two solutions are:

xy = -6, and xy = 3

If we sub in xy = 3, we get X^2 = 9/y^2

But, if we sub in xy = -6, we get X^2 = 36/y^2, which is also in the answer choices.

So what am I doing wrong?

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: PS: x^2   [#permalink] 21 Aug 2008, 12:56
Display posts from previous: Sort by