Let be the statement '' and be the statement ' for every real '. Which of the following is correct? (Here is a real number.)

Answer and explanation

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

  1. Step 1: has least value (at ).
  2. Step 2: So for all exactly when , i.e. : the statements are equivalent.
Answer
is both a necessary and a sufficient condition for .
Why not the others: There is no for which exactly one of the two statements holds, because both are equivalent to .

Practise more Necessary and sufficient conditions on a parameter.

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