The graph of touches the -axis at exactly one point, and . What is ?

Answer and explanation

Correct answer: E.

  1. Step 1: Touching the axis means a repeated root, so the discriminant is zero: .
  2. Step 2: Hence , and the condition leaves .
Answer
.
Why not the others: With or the discriminant is negative, so the graph misses the axis; with or it is positive, so the graph crosses the axis twice.

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