Q7 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

If the function fx=cos-1⁡x32-1-x-x2+x3 (where, ∀0<x<1), then the value of 3f'12 is equal to (take 3=1.73)

Correct answer: 3.73

Solution

fx=cos-1⁡xx-1-x1-x2
=cos-1⁡xx-1-x21-x2
=cos-1⁡x+cos-1⁡x
Now,  f ′ x = −1 1− x 2 − 1 1−x ⋅ 1 2 x
f'12=−11−14−112×1212=−23−1

3f'12=-3−23−1=3.73

 

Hence, the correct answer is 3.73.

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