Conditional Statements Lesson 2-1 Conditional Statements
Conditional Statements have two parts: Hypothesis (denoted by p) and Conclusion (denoted by q)
Conditional statements can be put into an “if-then” form to clarify which part is the hypothesis and which is the conclusion.
Hypothesis (p) Phrase following “if” the given information
Conclusion (q) Phrase following “then” the result of the given information
Example: can be written as... Vertical angles are congruent. If two angles are vertical, then they are congruent.
If two angles are vertical, then they are congruent. Hypothesis (p): two angles are vertical Conclusion (q): they are congruent p implies q
Conditional Statements can be true or false: A conditional statement is false only when the hypothesis is true, but the conclusion is false. A counterexample is an example used to show that a statement is not always true and therefore false.
Giving a Counterexample Statement: If you live in Virginia, then you live in Richmond. Is there a counterexample? I live in Virginia, BUT I live in Glen Allen. YES... Therefore () the statement is false.
Symbols can be used to modify or connect statements. Symbolic Logic Symbols can be used to modify or connect statements.
pq is used to represent if p, then q or p implies q
Example pq: If a number is prime, then it has exactly two divisors. p: a number is prime q: a number has exactly two divisors pq: If a number is prime, then it has exactly two divisors.
is used to represent the word ~ is used to represent the word “not”
Example p: the angle is obtuse ~p: the angle is not obtuse Be careful because ~p means that the angle could be acute, right, or straight
Example p: I am not happy ~p: I am happy Notice: ~p took the “not” out… it would have been a double negative (not not)
is used to represent the word is used to represent the word “and”
Example pq: A number is even and it is divisible by 3. p: a number is even q: a number is divisible by 3 pq: A number is even and it is divisible by 3. 6,12,18,24,30,36,42...
is used to represent the word is used to represent the word “or”
Example pq: A number is even or it is divisible by 3. p: a number is even q: a number is divisible by 3 pq: A number is even or it is divisible by 3. 2,3,4,6,8,9,10,12,14,15,...
is used to represent the word is used to represent the word “therefore”
Example Therefore, the statement is false. the statement is false
Different Forms of Conditional Statements
Converse: q p pq If two angles are vertical, then they are congruent. qp If two angles are congruent, then they are vertical.
Inverse: ~p~q pq If two angles are vertical, then they are congruent. ~p~q If two angles are not vertical, then they are not congruent.
Contrapositive:~q~p pq If two angles are vertical, then they are congruent. ~q~p If two angles are not congruent, then they are not vertical.
If pq is true, If pq is false, Contrapositives are logically equivalent to the original conditional statement. If pq is true, then qp is true. If pq is false, then qp is false.
Biconditional When a conditional statement and its converse are both true, the two statements may be combined. Use the phrase if and only if (iff)
Definitions are always biconditional Statement: If an angle is right then it has a measure of 90. Converse: If an angle measures 90, then it is a right angle. Biconditional: An angle is right iff it measures 90.