Thinking Mathematically Logic 3.1 Statements, Negations, and Quantified Statements
Statements A “statement” is a sentence that is either “true” or “false” but not both at the same time. Exercise Set 3.1 #3, 9 Statement? On January 20, 2009, John McCain became America’s 44 th president. Is the unexamined life worth living? = 16.
Statements - “Negation” The “negation” of a statement is another statement that has the opposite “truth value.” That is when a statement is true its negation is false and when the statement is false its negation is true. Exercise Set 3.1 #15 Form the negation of “It is raining” What is the negation of 2+2 = 5
Statements - “Symbolism” Just as x can be used as a name for a number, a symbol such as p can be used as a name for a statement. When p is used as a name for a statement the symbols ~p are used as a name for the negation of p.
Examples: Using Symbols for Statements Exercise Set 3.1 #23 p: One works hard q: One succeeds r: The temperature outside is not freezing s: It is not true that the heater is working The temperature outside is freezing = ? Exercise Set 3.1 #27 p: Listening to classical music makes infants smarter. q: Subliminal advertising makes you buy things. r: Sigmund Freund’s father was not 20 years older than his mother. s: Humans and bananas do not share approximately 60% of the same DNA structure. ~r = ?
“Quantified” Statements A “quantified” statement is one that says something about “all”, “some”, or “none” of the objects in a collection. Exercise Set 3.1 #29, #31, #35 For each of the statements: All whales are mammals. Some students are business majors. No Democratic presidents have been impeached. Give an equivalent statement Negate the statement.
Thinking Mathematically Logic 3.1 Statements, Negations, and Quantified Statements