GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 19 Oct 2019, 00:08

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

When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?

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

Hide Tags

Find Similar Topics 
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 8017
GMAT 1: 760 Q51 V42
GPA: 3.82
When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 25 Mar 2019, 00:31
00:00
A
B
C
D
E

Difficulty:

  85% (hard)

Question Stats:

29% (01:42) correct 71% (02:10) wrong based on 35 sessions

HideShow timer Statistics

[GMAT math practice question]

When \(f(x)=\frac{x^3+1}{x^3}\), which of the following is equal to \(f(\frac{-1}{x})\)?

\(A. f(x)\)
\(B. -f(x)\)
\(C. \frac{1}{f(x)}\)
\(D. 1-f(x)\)
\(E. (f(x))^3\)

_________________
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.
"Only $79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 12 Sep 2015
Posts: 4009
Location: Canada
When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 25 Mar 2019, 06:59
1
Top Contributor
MathRevolution wrote:
[GMAT math practice question]

When \(f(x)=\frac{x^3+1}{x^3}\), which of the following is equal to \(f(\frac{-1}{x})\)?

\(A. f(x)\)
\(B. -f(x)\)
\(C. \frac{1}{f(x)}\)
\(D. 1-f(x)\)
\(E. (f(x))^3\)


GIVEN: f(x)=(x³ + 1)/x³
So, f(-1/x) = [(-1/x)³ + 1]/(-1/x
= (-1/x³ + 1)/(-1/x³)
= (-1/x³)/(-1/x³) + (1)/(-1/x³)
= 1 - x³

Hmmm, am I missing something?

Cheers,
Brent
_________________
Test confidently with gmatprepnow.com
Image
GMAT Club Legend
GMAT Club Legend
User avatar
D
Joined: 18 Aug 2017
Posts: 5020
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Premium Member
Re: When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 25 Mar 2019, 09:01
1
MathRevolution wrote:
[GMAT math practice question]

When \(f(x)=\frac{x^3+1}{x^3}\), which of the following is equal to \(f(\frac{-1}{x})\)?

\(A. f(x)\)
\(B. -f(x)\)
\(C. \frac{1}{f(x)}\)
\(D. 1-f(x)\)
\(E. (f(x))^3\)


solving for \(f(\frac{-1}{x})\)
will give = (1-x^3)

I am not sure how B is coming out correct as \(-f(x)\) = 1-x^3/ x^3
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 8017
GMAT 1: 760 Q51 V42
GPA: 3.82
When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 27 Mar 2019, 01:01
=>


\(f(\frac{-1}{x}) = (\frac{-1}{x})^3 + 1/{1/(\frac{-1}{x})^3} = \frac{-1}{x^3} – x^3 = -(x^3+\frac{1}{x^3}) = -f(x).\)

Therefore, B is the answer.
Answer: B
_________________
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.
"Only $79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Manager
Manager
avatar
B
Joined: 09 Jun 2017
Posts: 105
GMAT 1: 640 Q44 V35
Re: When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 29 Mar 2019, 04:23
let x be 1
f(1) = 1+1 \ 1 = 2
f(-1/x) =f(-1) = 0
can't find any correct answer !
_________________
Hope this helps
Give kudos if it does
Manager
Manager
User avatar
G
Joined: 21 Feb 2019
Posts: 125
Location: Italy
Premium Member
Re: When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 29 Mar 2019, 06:33
1
MathRevolution wrote:
=>


\(f(\frac{-1}{x}) = (\frac{-1}{x})^3 + 1/{1/(\frac{-1}{x})^3} = \frac{-1}{x^3} – x^3 = -(x^3+\frac{1}{x^3}) = -f(x).\)

Therefore, B is the answer.
Answer: B


I still don't understand. Shouldn't it be, in the first passage, \((\frac{-1}{x})^3 + 1/{(\frac{-1}{x})^3}\)?
_________________
If you like my post, Kudos are appreciated! Thank you.


MEMENTO AUDERE SEMPER
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 8017
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?  [#permalink]

Show Tags

New post 31 Mar 2019, 13:27
lucajava wrote:
MathRevolution wrote:
=>


\(f(\frac{-1}{x}) = (\frac{-1}{x})^3 + 1/{1/(\frac{-1}{x})^3} = \frac{-1}{x^3} – x^3 = -(x^3+\frac{1}{x^3}) = -f(x).\)

Therefore, B is the answer.
Answer: B


I still don't understand. Shouldn't it be, in the first passage, \((\frac{-1}{x})^3 + 1/{(\frac{-1}{x})^3}\)?


We plugged in \(-\frac{1}{x}\) for x.
_________________
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.
"Only $79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
GMAT Club Bot
Re: When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?   [#permalink] 31 Mar 2019, 13:27
Display posts from previous: Sort by

When f(x)=x^3+1/x^3, which of the following is equal to f(-1/x)?

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





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