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Logic

Logic. To write a conditional To identify the hypothesis and conclusion in a conditional To write the converse, inverse and contrapositive of a given conditional To state the truth value of each of the above (draw conclusions) To write a biconditional.

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Logic

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  1. Logic To write a conditional To identify the hypothesis and conclusion in a conditional To write the converse, inverse and contrapositive of a given conditional To state the truth value of each of the above (draw conclusions) To write a biconditional

  2. Conditional- an if-then statementWrite a conditional with each of the following: • A right angle has a measure = 90◦. • If an angle is a rt. <, then it = 90◦. • If an < = 90◦, then it is a rt. <. • Christmas is on December 25th. • If it is Christmas, then it is Dec. 25th. • If it is Dec. 25th, then it is Christmas.

  3. Every conditional has a hypothesis and a conclusion. The hypothesis always follows the if and the conclusion always follows the then. Underline the hypothesis once and the conclusion twice for the previous statements.

  4. Conditional- an if-then statementWrite a conditional with each of the following: • A right angle has a measure = 90◦. • If an angle is a rt. <, then it = 90◦. • If an < = 90◦, then it is a rt. <. • Christmas is on December 25th. • If it is Christmas, then it is Dec. 25th. • If it is Dec. 25th, then it is Christmas.

  5. The following is a Venn diagram. Use it to write a conditional. If you are a teacher, then you have at least a 4 year college degree. At least a 4 year college degree Teacher

  6. Write a conditional. If you are a chow, then you are a dog.

  7. Counterexamples-examples for which a conjecture (statement) is incorrect. If it is a weekday, then it is Monday. counterexample– it could be Tuesday If the animal is a dog, then it is a poodle. counterexample--- it could be a lab If a number is prime it is not even. counterexample---2 is a prime #

  8. Define converse, inverse, and contrapositive of a given conditional. Converse of a conditional ----flips the hypothesis and conclusion Inverse of a conditional-----negates both the hypothesis and conclusion Contrapositive of a conditional ----flips and negates the conditional

  9. Logic Symbols • Conditional p → q • Converse q → p Flips conditional • Inverse ~p → ~q negates conditional • Contrapositive ~q → ~p flips and negates conditional

  10. If 2 segments are congruent, then they are equal in length. • Write the converse, inverse,& contrapositive for the above statement. Converse---- If 2 segments are equal in length, then they are congruent. Inverse-----If 2 segments are not congruent, then they are not equal in length. Contrapositive---- If 2 segments are not equal in length, then they are not congruent.

  11. If 2 angles are vertical, then they are congruent. • Write the 1.converse 2. inverse 3. contrapositive. • If 2 angles are congruent, then they are vertical. • If 2 angles are not vertical, then they are not congruent. • If 2 angles are not congruent, then they are not vertical.

  12. Write the 1.converse 2. inverse 3. contrapositive of the following definition If an angle is a right angle, then the angle is equal to 90 degrees. If an angle is equal to 90 degrees, then it is a right angle. If an angle is not a right angle, then it is not equal to 90 degrees. If an angle is not equal to 90 degrees then it is not a right angle.

  13. Go back and determine the truth values of all your problems. Do you notice anything?

  14. If 2 segments are congruent, then they are equal in length. • Write the converse, inverse,& contrapositive for the above statement. Converse---- If 2 segments are equal in length, then they are congruent. Inverse-----If 2 segments are not congruent, then they are not equal in length. Contrapositive---- If 2 segments are not equal in length, then they are not congruent. Note the above is a definition!!!!

  15. If 2 angles are vertical, then they are congruent. • Write the 1.converse 2. inverse 3. contrapositive. • If 2 angles are congruent, then they are vertical. • If 2 angles are not vertical, then they are not congruent. • If 2 angles are not congruent, then they are not vertical. • Note the above is a theorem!!!!

  16. Write the 1.converse 2. inverse 3. contrapositive of the following definition If an angle is a right angle, then the angle is equal to 90 degrees. If an angle is equal to 90 degrees, then it is a right angle. If an angle is not a right angle, then it is not equal to 90 degrees. If an angle is not equal to 90 degrees then it is not a right angle.

  17. Truth Values • The conditionaland the contrapositivealways have the same truth value. • The converse and the inverse always have the same truth value.

  18. Truth Values • Note the truth values are all true if your conditional started with a definition. • This is not necessarily true for a theorem.

  19. D Isosceles Triangle Theorem If 2 sides of a triangle are congruent, then the angles opposite those sides are congruent. B A If DB ≅ DA then, <B ≅ < A.

  20. Converse of Isosceles Triangle Theorem If 2 <‘s of a triangle are congruent, then the sides opposite those angles are congruent. D B A If <B ≅ < A, then BD ≅ DA.

  21. Biconditional- a statement that combines a true conditional with its true converse in an if and only if statement.Conditional- If an < is a rt <, then it = 90◦converse If an < = 90◦, then it is a right <. • An angle is a right angle if and only if it is equal to 90 degrees. • An angle is equal to 90 degrees iff it is a right angle.

  22. Write a biconditional. • If 3 points lie on the same line, then they are collinear. • If 3 points are collinear, then they lie on the same line. • 3 points are collinear if and only if they lie on the same line • 3 points are on the same line if and only if they are collinear.

  23. Write a biconditional. • If 2 lines are skew, then they are noncoplanar. • If 2 lines are noncoplanar, then they are skew. • 2 lines are noncoplanar iff they are skew. • 2 lines are skew iff they are noncoplanar.

  24. Write a converse, inverse, contrapositive and biconditional for the following: If 2n = 8, then 3n = 12. Converse If 3n = 12, then 2n = 8. Inverse If 2n ≠ 8, then 3n ≠ 12. Contrapositive If 3n ≠ 12, then 2n ≠ 8. 2n = 8 iff 3n = 12 3n = 12 iff 2n = 8

  25. Note every definition is biconditional!

  26. Rewrite as 2 if-then statements (conditional and converse) (x+4) ( x-5) = 0 iff x= -4 or x= 5 If (x+4) (x-5) = 0 then x= -4 or x= 5. If x = -4 or x = 5, then (x+4) ( x-5) = 0.

  27. Write the converse of the given conditional, then write 2 biconditionals • 1. If a point is a midpoint, then it divides a segment into 2 congruent halves. If a point divides a segment into 2 ¤ halves, then it is a midpoint. A pt. is a midptiff it divides a segment into 2 ¤ halves. A pt. divides a segment into 2 ¤ halves iff it is a midpoint.

  28. Assignments Homework---pp.71-73 (2-4;9-12;15-29;33-35) p. 78 (1-11 0dd) p 267 (1-9 odd) Classwork– HM worksheet # 11

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