Let be the statement 'the quadratic has real roots' and be the statement ''. Which of the following is correct? (Here and are real numbers.)

Answer and explanation

Correct answer: B. is both a necessary and a sufficient condition for

  1. Step 1: Real roots need .
  2. Step 2: Rearranging gives , so the two statements are equivalent.
Answer
is both a necessary and a sufficient condition for .
Why not the others: The condition on is just the discriminant condition rearranged; the statements are true for exactly the same pairs .

Practise more Necessary and sufficient conditions.

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