It is currently 18 Jan 2018, 04:01

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If x - 7 = √x + √7 , x = ?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Expert Post
Math Revolution GMAT Instructor
User avatar
D
Joined: 16 Aug 2015
Posts: 4683

Kudos [?]: 3313 [0], given: 0

GPA: 3.82
Premium Member
If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 21 Aug 2017, 00:26
Expert's post
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

60% (01:58) correct 40% (03:11) wrong based on 85 sessions

HideShow timer Statistics

If \(x - 7 = √x + √7\) , x = ?

A. 8 + 2√7
B. 8 - 2√7
C. 8 + √7
D. 8 - √7
E. 7 + 2√8
[Reveal] Spoiler: OA

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself
See our Youtube demo


Last edited by Bunuel on 21 Aug 2017, 00:55, edited 1 time in total.
Renamed the topic and edited the question.

Kudos [?]: 3313 [0], given: 0

Senior CR Moderator
User avatar
V
Status: Long way to go!
Joined: 10 Oct 2016
Posts: 1317

Kudos [?]: 1185 [0], given: 62

Location: Viet Nam
GMAT ToolKit User Premium Member CAT Tests
Re: If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 21 Aug 2017, 00:32
1
This post was
BOOKMARKED
MathRevolution wrote:
If x-7=√x+√7 , x=?

A. 8+2√7 B. 8-2√7 C. 8+√7 D. 8-√7 E. 7+2√8


\(x-7=\sqrt{x}+\sqrt{7} \implies (\sqrt{x}+\sqrt{7})(\sqrt{x}-\sqrt{7}) = \sqrt{x}+\sqrt{7} \implies (\sqrt{x}+\sqrt{7})(\sqrt{x}-\sqrt{7} -1)=0 \)
thus \(\sqrt{x}+\sqrt{7}=0\) or \(\sqrt{x}-\sqrt{7} -1=0\)
thus \(\sqrt{x}=\sqrt{7} +1 \implies x= 8+2\sqrt{7}\)

Answer A
_________________

Actual LSAT CR bank by Broall

How to solve quadratic equations - Factor quadratic equations
Factor table with sign: The useful tool to solve polynomial inequalities
Applying AM-GM inequality into finding extreme/absolute value

New Error Log with Timer

Kudos [?]: 1185 [0], given: 62

Expert Post
Math Revolution GMAT Instructor
User avatar
D
Joined: 16 Aug 2015
Posts: 4683

Kudos [?]: 3313 [0], given: 0

GPA: 3.82
Premium Member
Re: If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 23 Aug 2017, 00:21
=> x-7=√x+√7
(√x+√7 )(√x-√7)=√x+√7
√x-√7=1
√x = 1 +√7
x = (1 +√7)2 = 8 +2√7

Ans: A
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself
See our Youtube demo

Kudos [?]: 3313 [0], given: 0

Director
Director
User avatar
P
Joined: 18 Aug 2016
Posts: 627

Kudos [?]: 208 [0], given: 166

Concentration: Strategy, Technology
GMAT 1: 630 Q47 V29
GMAT 2: 740 Q51 V38
GMAT ToolKit User Premium Member Reviews Badge
Re: If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 29 Aug 2017, 01:49
MathRevolution wrote:
If \(x - 7 = √x + √7\) , x = ?

A. 8 + 2√7
B. 8 - 2√7
C. 8 + √7
D. 8 - √7
E. 7 + 2√8


\(x - 7 = √x + √7\)
\((√x + √7) (√x - √7) = √x + √7\)
\((√x - √7) = 1\)
\(\sqrt{x} = 1 + √7\)
\(x= 1+7+2\sqrt{7}\)
A
_________________

We must try to achieve the best within us


Thanks
Luckisnoexcuse

Kudos [?]: 208 [0], given: 166

Manager
Manager
avatar
S
Joined: 05 Oct 2016
Posts: 76

Kudos [?]: 40 [0], given: 120

Location: United States (OH)
GPA: 3.58
CAT Tests
Re: If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 29 Aug 2017, 18:01
please provide in depth explanation of this please
_________________

Kudos APPRECIATED!

Kudos [?]: 40 [0], given: 120

1 KUDOS received
Director
Director
User avatar
P
Joined: 04 Dec 2015
Posts: 696

Kudos [?]: 354 [1], given: 261

Location: India
Concentration: Technology, Strategy
Schools: ISB '19, IIMA , IIMB, XLRI
WE: Information Technology (Consulting)
GMAT ToolKit User CAT Tests
If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 29 Aug 2017, 19:55
1
This post received
KUDOS
MathRevolution wrote:
If \(x - 7 = √x + √7\) , x = ?

A. 8 + 2√7
B. 8 - 2√7
C. 8 + √7
D. 8 - √7
E. 7 + 2√8


SandhyAvinash wrote:
please provide in depth explanation of this please

\((x - 7)\) can be written in \((a^2 - b^2) = (a+b)(a-b)\) format. Where; \((x - 7)\) is \((a^2 - b^2)\)

Therefore; \((x - 7) = (√x + √7)(√x - √7)\)

\(x - 7 = √x + √7\)

\((√x + √7)(√x - √7) = √x + √7\)

\((√x - √7) = \frac{(√x + √7)}{(√x + √7)}\)

\(√x - √7 = 1\)

\(√x = 1 + √7\)

Squaring both sides we get;

\((√x)^2 = (1 + √7)^2\)

\(x = 1 + 7 + 2√7\)

\(x = 8 + 2√7\)

Answer (A)...

Hope its clear now... :-)

Kudos [?]: 354 [1], given: 261

Director
Director
User avatar
P
Joined: 13 Mar 2017
Posts: 560

Kudos [?]: 145 [0], given: 64

Location: India
Concentration: General Management, Entrepreneurship
GPA: 3.8
WE: Engineering (Energy and Utilities)
Re: If x - 7 = √x + √7 , x = ? [#permalink]

Show Tags

New post 29 Aug 2017, 22:37
MathRevolution wrote:
If \(x - 7 = √x + √7\) , x = ?

A. 8 + 2√7
B. 8 - 2√7
C. 8 + √7
D. 8 - √7
E. 7 + 2√8


\(x - 7 = √x + √7\)
(√x + √7)(√x - √7) = √x + √7
√x - √7 = 1
√x = 1 + √7
x = 1 + 7 + 2√7 = 8 + 2√7

Answer A
_________________

MBA Social Network : WebMaggu

Appreciate by Clicking +1 Kudos ( Lets be more generous friends.)

Kudos [?]: 145 [0], given: 64

Re: If x - 7 = √x + √7 , x = ?   [#permalink] 29 Aug 2017, 22:37
Display posts from previous: Sort by

If x - 7 = √x + √7 , x = ?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.