Contrapositive, Inverse, and Converse Lesson 2.1
Counterexample Consider question 3a on the Do Now. An EXAMPLE that proves the conjecture is false. (note: a counterexample simply disproves a statement but does NOT prove the converse)
Clear Boards OUT! If a number is prime, then it is even If two angles are acute, then they are congruent
Notation Conditional Statement “If p then q” Negation “not p” Example: if p is “it is raining” then p is “it is not raining Converse “If q then p” Inverse “If not p then not q” Contrapositive “If not q then not p”
What is Truth?!?!?!
Example 1 Consider the statement: If you live in Newark, then you live in New Jersey Find: Converse: Inverse: Contrapositive:
Analyze each statement. Is it true? What conclusions can we draw? You Try! Find the converse, inverse, and contrapositive of each of the following statements. If a person is 18 years old, then he or she may vote in federal elections. If angles are right angles then they are congruent If an angle is a right angle, then it measures 90. Analyze each statement. Is it true? What conclusions can we draw?
If the conditional statement is true, then the contrapositive is true. If the statement is a definition, then the converse, inverse, and contrapositive are all true. (Definitions are said to be reversible) If the statement is a theorem, the converse and inverse are not (necessarily) true.