 It is currently 25 Aug 2019, 08:05 ### 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. # x2 + y2 = 81 x2 - y2 = 0  Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
Founder  Joined: 18 Apr 2015
Posts: 7810
Followers: 145

Kudos [?]: 1608 , given: 7073

x2 + y2 = 81 x2 - y2 = 0 [#permalink]
Expert's post 00:00

Question Stats: 83% (00:44) correct 16% (00:12) wrong based on 6 sessions
$$x^2 + y^2 = 81$$

$$x^2 - y^2 = 0$$

 Quantity A Quantity B $$x^4-y^4$$ $$0$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________ GRE Instructor Joined: 10 Apr 2015
Posts: 2311
Followers: 73

Kudos [?]: 2208  , given: 27

Re: x2 + y2 = 81 x2 - y2 = 0 [#permalink]
1
This post received
KUDOS
Expert's post
Carcass wrote:
$$x^2 + y^2 = 81$$

$$x^2 - y^2 = 0$$

 Quantity A Quantity B $$x^4-y^4$$ $$0$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

Nice question!
I like it because we can ignore the first equation, and just use the second equation.

Take: $$x^2 - y^2 = 0$$
Add $$y^2$$ to both sides to get: $$x^2 = y^2$$
Square both sides to get: $$(x^2)^2 = (y^2)^2$$
Simplify by applying the Power of a Power law to get: $$x^4 = y^4$$
Rewrite as follows: $$x^4 - y^4 = 0$$

Answer: C

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Day emails Intern Joined: 15 Aug 2019
Posts: 31
Followers: 0

Kudos [?]: 20  , given: 3

Re: x2 + y2 = 81 x2 - y2 = 0 [#permalink]
1
This post received
KUDOS
# (A+B) * (A-B) = A^2 - B^2
So (x^2+y^2) * (x^2-y^2) = (x^4-y^4)
=> 81 * 0 => 0
Ans is C. Re: x2 + y2 = 81 x2 - y2 = 0   [#permalink] 17 Aug 2019, 02:15
Display posts from previous: Sort by

# x2 + y2 = 81 x2 - y2 = 0  Question banks Downloads My Bookmarks Reviews Important topics  Powered by phpBB © phpBB Group Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.