Exercise · ZW-NEGATION-OF-QUANTIFIERS-008 · ★★☆ Intermediate
To negate 'every number is positive' it is enough to state...
Choose one option.
Show answer
- B. There is a number that is not positive
Explanation
Negating 'every number is positive' requires a number that is not positive: \(\exists x\,\neg P(x)\), i.e., there is a non-positive number.
Review the concept: Negation of quantifiers
For a predicate \(P(x)\) over \(D\), negating a quantifier swaps the quantifier and negates the predicate.
\[\begin{gathered}\neg\forall x P(x)\equiv\exists x\neg P(x)\\\neg\exists x P(x)\equiv\forall x\neg P(x)\end{gathered}\]
More practice problems: negation of quantifiers
- ZW-NEGATION-OF-QUANTIFIERS-001 The negation of ∀ x P(x) is...
- ZW-NEGATION-OF-QUANTIFIERS-002 The negation of ∃ x P(x) is...
- ZW-NEGATION-OF-QUANTIFIERS-003 "Not all students passed" is equivalent to...
- ZW-NEGATION-OF-QUANTIFIERS-004 What operation appears when negating a quantifier?
- ZW-NEGATION-OF-QUANTIFIERS-005 Which equivalence is correct?
- ZW-NEGATION-OF-QUANTIFIERS-006 The negation of ∀ x P(x) is equivalent to...
- ZW-NEGATION-OF-QUANTIFIERS-007 The negation of ∃ x P(x) is equivalent to...
- ZW-NEGATION-OF-QUANTIFIERS-009 Select the correct equivalence.
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