Q39 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

If f x = 2+x 1+x 1+x , then f ′ 0 is equal to

  • A
    2log2
  • B
    log2
  • C
    3log2−1
  • Correct answer
    D
    2log2−1

Solution

By taking logarithm on both sides, 
 logf(x) = (1+x) log(2+x)−log(1+x) 
On differentiating, we get, 

1fx·f'x=1+x2+x+log(2+x)−1+x1+x−log(1+x)

Now, put x=0

f'(0)=f01+log22−1=f0log2−12

=2log2−1 ∵f 0 =2

Hence, the correct answer is option: 'D'.

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