Q40 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

If fx=2sin⁡x-1-2cot⁡x, then the value of f'π3 is equal to

  • A
    0
  • B
    -53
  • Correct answer
    C
    53
  • D
    83

Solution

In the neighbourhood of x=π3, we know,

2sin⁡x-1>0
⇒fx=2sin⁡x-1-2cot⁡x
Now, for the neighbourhood of x=π3
2sin⁡x-1-2cot⁡x=232-1-23=3-23-1
=13-1<0
∴fx=2cot⁡x-2sin⁡x-1
Now, f'x=2-cosec2x-2cos⁡x
f'π3=2-232-212
=243-1=53

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

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