The line is a tangent to the curve . What is the positive value of ?

Answer and explanation

Correct answer: B.

  1. Step 1: Set equal: . A tangent gives discriminant .
  2. Step 2: so , giving or .
  3. Step 3: The positive value is .
Answer
.
Why not the others: The discriminant of is . It is for and for (no contact) and and for and (two intersections), so none of these gives a tangent.

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