Understanding Conditional Statements in Algebra

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3. Lesson 2 - 2 Conditional Statements, Converses, Inverses, Contrapositives

4. Chart for Algebra Dummies Like Me

5. Conditional StatementsIf . . . Then • Conditional Statement – A compound statement formed by combining two sentences (or facts) using the words “if…then.” Example: If you pass all of your tests, then you will pass the class.

6. Definitions • Hypothesis: The part of the sentence that follows the word “IF” • Conclusion: The part of the sentence that follows the word “THEN”

7. EXAMPLE: If you do your homework on time, then you will have a better grade. What is the hypothesis? you do your homework on time What is the conclusion? you will have a better grade

8. It may be necessary to rewrite a sentence so that it is in conditional form (“if” first, “then” second). Example: All surfers like big waves. Rewrite as a conditional statement. If you are a surfer, then you like big waves.

9. Truth Value • When you determine whether a conditional statement is true or false, you determine its truth value.

10. Counterexamples • Counterexample: An example that proves a statement false Write a counterexample for the following conditional statement: If a student likes math, then he likes chemistry.

11. Converse • Converse of a Conditional Statement: Formed by interchanging the hypothesis and conclusion of the original statement. Example: Conditional: If the space shuttle was launched, then a cloud of smoke was seen. Converse: If a cloud of smoke was seen, then the space shuttle was launched.

12. HINT Try to associate the logical CONVERSE with Converse sneakers – think of the two parts of the sentence “putting on their sneakers and running to their new positions.”

13. Inverse • Inverse of a Conditional Statement: formed by negating the hypothesis and negating the conclusion of the original statement. • Put “not” into the hypothesis and the conclusion

14. Example • Conditional: If you grew up in Alaska, then you have seen snow. • Inverse: If you did not grow up in Alaska, then you have not seen snow. HINT: Hint: To create an INverse, you need to INsert the word not into both the hypothesis and the conclusion. Does the truth value of an inverse have to be the same as the truth value of the original conditional statement?

15. Contrapositive Contrapositive of a Conditional Statement: • formed by negating both the hypothesis and the conclusion and then interchanging the resulting negations. • Put “not” into the hypothesis and the conclusion, then switch the order.

16. Example • Conditional: If 8 is an even number, then 8 is divisible by 2. • Contrapositive: If 8 is not divisible by two, then 8 is not an even number.

17. HINT • For contrapositive, combine both converse and inverse. • The truth value of a contrapositive is ___________________ the original conditional statement. The same as

18. Conditional, Converse, Inverse, and Contrapositive For each statement, write the (a) converse, (b) inverse, and (c) the contrapositive. Give the truth value for each statement. 1. If a student is on the University of Arkansas football team, then he is called a Razorback . If a student is called a Razorback, then he is on the University of Arkansas football team. If a student is not on the University of Arkansas football team, then he is not called a Razorback. If a student is not called a Razorback, then he is not on the University of Arkansas football team. a False b False c True

19. Conditional, Converse, Inverse, and Contrapositive For each statement, write the (a) converse, (b) inverse, and (c) the contrapositive. Give the truth value for each statement. 2. If a person skateboards, then she has a sense of balance. If a person has a sense of balance, then she skateboards. FALSE If a person does not skateboard, then she does not have a sense of balance. FALSE If a person does not have a sense of balance, then she does not skateboard. TRUE a b c

20. Conditional, Converse, Inverse, and Contrapositive For each statement, write the (a) converse, (b) inverse, and (c) the contrapositive. Give the truth value for each statement. 3. If it thunderstorms, then our pond overflows. If our pond overflows, then it has thunderstormed. FALSE If it does not thunderstorm, then our pond will not overflow. FALSE If our pond does not overflow, then it has not thunderstormed. TRUE a b c

21. Assignment • Lesson 2-3 p.78 #16-44 ev, 50-51

22. Venn Diagrams • A Venn diagram is a drawing used to represent a set of numbers or conditions. Venn diagrams can be useful in explaining conditional statements.

23. Hypothesis Conclusion Example If hypothesis, then conclusion. If the cows are laying down, then it is going to rain. Cows arelaying down It is going to rain

24. Equilateral Triangles Squares Triangles with 3 acute angles Quadrilaterals Parallelogram with perpendicular diagonals Rhombus Write the conditional statement from the Venn diagram. If an object is an equilateral triangle, then it has three acute angles. If an object is a square, then it is a quadrilateral. If a parallelogram has perpendicular diagonals, then it is a rhombus.