JEE Main · 2020 · 09 Jan 2020 · Shift 2 · Differentiation

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Let and be differentiable functions on such that fog is the identity function. If for some and , then is equal to:
  1. (A)1
  2. (B)5
  3. (C)✓ Correct
  4. (D)

Answer: (C)

Solution

Since is the identity, for all . Differentiating by the chain rule gives . Evaluating at , where and , this becomes , so .

JEE Main · 2020 · 09 Jan 2020 · Shift 2 · Single correct option

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