Let . Find the set of all real values of for which is strictly increasing on .

Answer and explanation

Correct answer: D.

  1. Step 1: Strictly increasing needs with equality at isolated points only.
  2. Step 2: The smallest value of is , so .
  3. Step 3: At the gradient is zero only at isolated points, so is still strictly increasing; is included.
Answer
k >= 2.
Why not the others: wrongly excludes the end value; ignores the factor 2 from the chain rule; the closed interval describes the range of , not the condition.

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