It is currently 20 Apr 2019, 06:19

### 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

# (x - 2y)(x + 2y) = 4

Author Message
TAGS:
Founder
Joined: 18 Apr 2015
Posts: 6198
Followers: 99

Kudos [?]: 1199 [1] , given: 5708

(x - 2y)(x + 2y) = 4 [#permalink]  01 Feb 2017, 06:51
1
KUDOS
Expert's post
00:00

Question Stats:

82% (00:20) correct 17% (00:54) wrong based on 39 sessions

$$(x - 2y)(x + 2y) = 4$$

 Quantity A Quantity B $$x^2 - 4y^2$$ $$8$$

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

_________________
GRE Prep Club Legend
Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 106

Kudos [?]: 1820 [1] , given: 397

Re: (x - 2y)(x + 2y) = 4 [#permalink]  06 Feb 2017, 09:28
1
KUDOS
Expert's post
Explanation

We know that, $$(x + y)(x - y) = x^2 - y^2$$

So we can rewrite the:

$$(x + 2y)(x - 2y) = x^2 - 4y^2 = 4$$

They can quickly compare 4 to 8 and determine B is greater.

If you forget the classic quadratic form, simply perform (first, outer, inner, last):

(x + 2y)(x - 2y) → $$x^2 - 2xy + 2xy - 4y^2 = 4$$ → $$x^2 - 4y^2 = 4$$

Compare the quantities: Quantity A: 4 Quantity B: 8

Hence option B is correct.
_________________

Sandy
If you found this post useful, please let me know by pressing the Kudos Button

Try our free Online GRE Test

GRE Instructor
Joined: 10 Apr 2015
Posts: 1647
Followers: 57

Kudos [?]: 1572 [1] , given: 8

Re: (x - 2y)(x + 2y) = 4 [#permalink]  15 Feb 2019, 11:08
1
KUDOS
Expert's post
Carcass wrote:

$$(x - 2y)(x + 2y) = 4$$

 Quantity A Quantity B $$x^2 - 4y^2$$ $$8$$

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

GIVEN: (x − 2y)(x + 2y) = 4
Use FOIL to expand left side: x² + 2xy - 2xy - 4y² = 4
Simplify left side: x² - 4y² = 4

We get:
QUANTITY A: 4
QUANTITY B: 8

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com

Re: (x - 2y)(x + 2y) = 4   [#permalink] 15 Feb 2019, 11:08
Display posts from previous: Sort by