inequality 2

if a1,a2,a3,....,an are +ve real nos whose product is a fixed real no. 'c',
then the minimum value of a1+a2+a3+......+2an-1 + 2an is --

a) n(4c)1/n

b) (n+1) c 1/n

c) 2nc1/n

d) (n+1)(2c)1/n

7 Answers

341
Hari Shankar ·

Direct AM-GM will give you option (a)

62
Lokesh Verma ·

where did u get 2an and 2an-1??

Is this not a typo?! :O

1
skygirl ·

no it is not a typo bhaiya..

dat is only my doubt!!

where from those came suddenly...

341
Hari Shankar ·

Ok, instead of 2an-1 and 2an write a'n-1 and a'n

Then the problem is:
Given +ve real nos. a1 a2a3....a'n-1a'n = 4c,

find the maximum of

a1 + a2+ a3+...+a'n-1+ a'n

This you know how to solve

62
Lokesh Verma ·

yeah that is ok prophet.. but how can we be sure how only the last 2 terms are 2.an not the other terms in between! :O

341
Hari Shankar ·

I didnt have reason to suspect, because the answer tallied with option (a) :D

Otherwise skygirl would have had a lot to answer for :D :D

62
Lokesh Verma ·

yup gotcha ;)

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