Application of Derivatives 4 Question 16

17. If x=1 and x=2 are extreme points of f(x)=αlog|x|+βx2+x, then

(a) α=6,β=12

(b) α=6,β=12

(c) α=2,β=12

(d) α=2,β=12

(2014 Main)

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Answer:

Correct Answer: 17. (c)

Solution:

  1. Here, x=1 and x=2 are extreme points of f(x)=αlog|x|+βx2+x, then

f(x)=αx+2βx+1f(1)=α2β+1=0

[at extreme point, f(x)=0 ]

f(2)=α2+4β+1=0

On solving Eqs. (i) and (ii), we get

α=2,β=12



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