1. 2.3 Using Deductive Reasoning to Verify Conjectures
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2.3 Using Deductive Reasoning to Verify Conjectures
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The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

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Deductive Reasoning
Deductive Reasoning: process of using logic to draw conclusions from given facts, definitions, and properties
Examples: Is each conclusion a result of inductive
or deductive reasoning?
There is a myth that you can balance an egg on its end only on the spring equinox. A person was able to balance an egg on July 8, September 21, and December 19. Therefore, this myth is false.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

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There is a myth that the Great wall of China is the only manmade object visible for the Moon. The Great Wall is barely visible in photographs taken from 180 miles above Earth. The Moon is about 237,000 miles from Earth. Therefore, the myth cannot be true.
There is a myth that an eel skin wallet will demagnetize credit cards because the skin of the electric eels used to make the wallets holds an electric eels. However, eel skin products are not made from electric eels. Therefore the myth cannot be true.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

4. Deductive Reasoning
Law of Detachment

5. Examples: Determine if the each conjecture is valid by the
Law of Detachment.
Given: If a student passes his classes, the student is eligible to play sports. Ramon passed his classes.
Conjecture: Ramon is eligible to play sports.
Given: If the side lengths of a triangle are 5 cm, 12 cm, and 13 cm, then the are of the triangle is 30 cm2. The are of ABC is 30 cm2.
Conjecture: The side lengths of ABC are 5cm, 12cm, and 13cm.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

6. Examples Continue…
Given: In the World Series, if a team wins four games, then the team wins the series. The Tigers won four games in the world series.
Conjecture: The Tigers won the world series.

7. Deductive Reasoning
Law of Syllogism

8. Examples Determine if each conjecture is valid by the Law of Syllogism
Given: If a figure is a kite, then it is a quadrilateral. IF a figure is a quadrilateral, then it is a polygon.
Conjecture: If a figure is a kite, then it is a polygon.

9. Examples Continue…
Given: If an animal is a mammal, then it has hair. If an animal is a dog, then it is a mammal.
Conjecture: If an animal is a dog, then it has hair.
Given: If a number is divisible by 2, then it is even. If a number is even, then it is divisible by 2.
Conjecture: If a number is an integer, then it is divisible by 2

10. Examples Draw a conclusion from the given information and
determine which law was used.
Given: If 2y=4, then z=-1. If x+3=12, then 2y=4. x+3=12
If the sum of the measures of two angles is 180o, then the angles are supplementary. If the two angles are supplementary, they are not angles of a triangle. Angle A=135o, and Angle B = 45o

11. Examples Continue… Draw a conclusion from the given information and
determine which law was used.
Given: If a polygon is a triangle, then it has three sides. If a polygon has three sides, then it is not a quadrilateral. Polygon P is a triangle