Let . If is differentiable at , what is the value of ?

Answer and explanation

Correct answer: B.

  1. Step 1: For to be differentiable at , it must be continuous at : .
  2. Step 2: Differentiability requires matching left-hand and right-hand derivatives at : , and . Equating them gives .
  3. Step 3: Substitute into the continuity equation: . Then evaluate .
Answer
.
Why not the others: Other values enforce continuity but ignore differentiability at the interface , or make arithmetic sign slips.

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