Logical Equivalence in Geometric Proofs
Understand the concepts of contrapositives, inverses, and logical implications in geometric proofs. Learn how to apply these principles to prove statements in geometry effectively.
Logical Equivalence in Geometric Proofs
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Presentation Transcript
Even Answers 2)(a)No (b)Yes (c)Yes (d)Yes (e)No (f)No 4)(a)Yes (b)Yes (c)No (d)No 6)(1)Given (2)CPCTC (3)Segment Addition Prop (4)Prop of Inequality (5)Substitution 8)(2)Segment Addition (3)Property of Inequality (4) Substitution 10)(2)Defintion ┴ lines (3)Exterior Angle Inequality Theorem (4)Substitution (5) Definition of Obtuse Angle
P: HYPOTHESIS Q: CONCLUSION • Statement If p, then q • Converse If q, then p • (con-artist—does a switch) • Inverse If not p, then not q • Add a word In---not • Contrapositive If not q, then not p • Weirdest word—so do both, add NOT and Switch
EXAMPLES: Give the Inverse and Contrapos. State Tor F 1. If a parallelogram is a square, then it is a rectangle. (T) I: If a parallelogram is not a square, then it is not a rectangle (F) C+: If a parallelogram is not a rectangle, then it is not a square (T) 2. If it is snowing, then the game is canceled. I: If it is not snowing, then the game is not canceled (F) C+: If the game is not canceled, then it is not snowing (T)
TRY ON OWN: 1. If I can sing, then you can dance. I: If I can’t sing, then you can’t dance (F) C+: If you can’t dance, then I can’t sing (T) 2. If Taylor is not here, then he is not well. I: If Taylor is here, then he is well (F) C+: If Taylor is well, then he is here (T)
Use a VENN DIAGRAM to tell if an assumption is True or False Example: All marathoners have stamina Statement: If you are a marathoner, then you have stamina • Nick is a marathoner • Heidi has stamina • Mimi does not have stamina • Arlo is not a marathoner He has stamina No conclusion She is not a marathoner No conclusion Marathoner Stamina
Try On Own: All Squares Are Rhombuses If it is a square, then it is a rhombus • ABCD is a Rhombus • PQRS is a square • LAST is not a rhombus • GHIJ is not a square What do we notice from this example & the last? 2 No Conclusions!! No Conclusion PQRS is a rhombus LAST is not a square No Conclusion Square Rhombus
RULE: The Statement and Contrapositive are logically equivalent! That means if the statement is True, the Contra+ is also True. The 2 others will be false.
HOMEWORK • Pg 210 #1-15 all