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M10-21

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M10-21  [#permalink]

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New post 15 Sep 2014, 23:42
1
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A
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58% (01:17) correct 42% (01:11) wrong based on 114 sessions

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The function \(f\) is defined by \(f(x) = - \frac{1}{x^2}\) for all nonzero numbers \(x\). If \(f(m) = - \frac{1}{16}\) and \(f(mn) = f(\frac{1}{n})\), what is the value of \(n^2\)?

A. \(\frac{1}{16}\)
B. \(\frac{1}{4}\)
C. \(\frac{1}{2}\)
D. \(2\)
E. \(4\)

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Re M10-21  [#permalink]

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New post 15 Sep 2014, 23:42
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Official Solution:

The function \(f\) is defined by \(f(x) = - \frac{1}{x^2}\) for all nonzero numbers \(x\). If \(f(m) = - \frac{1}{16}\) and \(f(mn) = f(\frac{1}{n})\), what is the value of \(n^2\)?

A. \(\frac{1}{16}\)
B. \(\frac{1}{4}\)
C. \(\frac{1}{2}\)
D. \(2\)
E. \(4\)


Since \(f(x) = - \frac{1}{x^2}\), then from \(f(m) = - \frac{1}{16}\) we'll have that \(-\frac{1}{m^2}=-\frac{1}{16}\), so \(m^2=16\).

The same way, from \(f(mn) = f(\frac{1}{n})\) we'll have that \(-\frac{1}{(mn)^2}=-n^2\), which simplifies to \(n^4=\frac{1}{m^2}\).

Since \(m^2=16\), then \(n^4=\frac{1}{m^2}=\frac{1}{16}\), which gives \(n^2=\frac{1}{4}\).


Answer: B
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Re: M10-21  [#permalink]

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New post 28 Oct 2015, 20:00
Hi Bunuel,

Can we now simply solve it like this? Since f(x)=−1/x^2, then from f(m)=−1/16 we'll have that −1/n^4=−1/16, so n^2=4.
As f(n^2) = -1/n^4.

Could you please explain if this is correct?
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Re: M10-21  [#permalink]

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New post 28 Oct 2015, 23:59
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Re M10-21  [#permalink]

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New post 25 Sep 2017, 23:52
Could you please elaborate on the following:
f(mn)=f(1/n) then we get -1/(mn)^2= - n^2. Don't understand who we got that result
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Re: M10-21  [#permalink]

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New post 25 Sep 2017, 23:56
d975490 wrote:
Could you please elaborate on the following:
f(mn)=f(1/n) then we get -1/(mn)^2= - n^2. Don't understand who we got that result


\(f(x) = - \frac{1}{x^2}\), hence \(f(mn) = -\frac{1}{(mn)^2}\) and \(f(\frac{1}{n})=-\frac{1}{(\frac{1}{n})^2}=-n^2\)
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Re: M10-21  [#permalink]

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New post 31 Oct 2017, 08:41
Bunuel wrote:
The function \(f\) is defined by \(f(x) = - \frac{1}{x^2}\) for all nonzero numbers \(x\). If \(f(m) = - \frac{1}{16}\) and \(f(mn) = f(\frac{1}{n})\), what is the value of \(n^2\)?

A. \(\frac{1}{16}\)
B. \(\frac{1}{4}\)
C. \(\frac{1}{2}\)
D. \(2\)
E. \(4\)



What sub-topic/tag does this question fall under? I am looking to solve similar question types both from the GMAT Club and the OG.
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Re: M10-21  [#permalink]

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New post 31 Oct 2017, 08:46
Edofarmer wrote:
Bunuel wrote:
The function \(f\) is defined by \(f(x) = - \frac{1}{x^2}\) for all nonzero numbers \(x\). If \(f(m) = - \frac{1}{16}\) and \(f(mn) = f(\frac{1}{n})\), what is the value of \(n^2\)?

A. \(\frac{1}{16}\)
B. \(\frac{1}{4}\)
C. \(\frac{1}{2}\)
D. \(2\)
E. \(4\)



What sub-topic/tag does this question fall under? I am looking to solve similar question types both from the GMAT Club and the OG.


Functions and algebra.

13. Functions




For more check Ultimate GMAT Quantitative Megathread

Hope it helps.
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re M10-21  [#permalink]

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New post 14 Sep 2018, 05:41
I think this is a high-quality question and I agree with explanation. I am quite sure that I marked Option B , but it shows that I have marked Option C.
I just hope it is a technical error. If it is kindly look into it,
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Re M10-21  [#permalink]

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New post 17 Nov 2018, 07:04
I think this is a high-quality question and I agree with explanation.
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Re M10-21 &nbs [#permalink] 17 Nov 2018, 07:04
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