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Negation of a logical statement

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Math for Non-Math Majors

Definition

A negation of a logical statement is the opposite of the original statement, often formed by adding 'not.' It changes a true statement to false and vice versa.

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5 Must Know Facts For Your Next Test

  1. Negating a universal quantifier (e.g., 'for all') results in an existential quantifier (e.g., 'there exists'), and vice versa.
  2. The negation of 'A and B' is 'not A or not B' based on De Morgan's laws.
  3. The negation of 'A or B' is 'not A and not B', also based on De Morgan's laws.
  4. Negating a conditional statement 'If A then B' results in 'A and not B'.
  5. Double negation returns the original statement, i.e., 'not (not A)' is equivalent to 'A'.

Review Questions

  • What is the negation of the statement: All students are present?
  • How do you negate the conditional statement: If it rains, I will stay home?
  • Apply De Morganโ€™s law to negate the following: Either it is raining, or it is snowing.

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