Inductive and Deductive Reasoning

Inductive and Deductive ReasoningNotecard 30Definition: Conjecture:an unproven statement that is based on observations or given information. Notecard 31Definition: Counterexample: a specific case for which a conjecture is false.

CounterexampleFind a counter example to show that the following conjecture is false.

The sum of two numbers is always greater than the larger number.

Notecard 32Definitions: Conditionals, Hypothesis, & Conclusions:A conditional statement is a logical statement that has two parts: If ____ then _____. The hypothesis is the if part and it tells you what you are talking about.

The conclusion is the then part and it describes the hypothesis.Writing a conditional statementWriting the following statements as conditionals.

Two angles that make a linear pair are supplementary.

All 90o angles are right angles.Notecard 33The negation of a statement is the opposite of the original.NegationNegate the following statements.

The ball is red.

The cat is not black.Notecard 34Definitions: Inverse, Converse, ContrapositiveThe converse of a conditional statement switches the hypothesis and conclusion.

The inverse of a conditional statement negates both the hypothesis and conclusion

The contrapositive of a conditional statement takes the inverse of the converse. (it switches and negates)Writing statementsWrite the converse, inverse and contrapositive of the conditional statement:

If two angles form a linear pair, then they are supplementary.

Which of these statements are true?Notecard 35Definition: Biconditional: If a conditional statement and its converse are both true, then we can write it as a biconditional statement by using the phrase if and only if instead of putting it in if-then form.

__________ if and only if ___________.(hypothesis) (conclusion)Biconditional StatementWrite the following conditional statement as a biconditional statement.

If two lines intersect to form a right angle, then they are perpendicular.The Law of DetachmentThis applies when one statement is conditional and a second statement confirms the hypothesis of the conditional. The conclusion is then confirmed.

Here is an example. Notecard 36If it is Friday, then Mary goes to the movies. It is Friday.

What conjecture can you make from the above statements?Deductive ReasoningIf two angles form a linear pair, then they are supplementary. Angle 1 and Angle 2 are a linear pair. Deductive ReasoningIf two angles form a linear pair, then they are supplementary. Angle 1 and Angle 2 are supplementary.

Deductive ReasoningThe Law of SyllogismThis applies when you have two conditional statements. The conclusion of one, confirms the hypothesis of the other. In this case our result is still a conditional with the first hypothesis and the second conclusion.

(I call this the Oreo Cookie Law.) Here is how it worksNotecard 37 If it is Friday, then Mary goes to the movies. If Mary goes to the movies then she gets popcorn.

Combine the two above conditional statements into one conditional statement.Deductive ReasoningIf two angles form a linear pair, then they are supplementary. If two angles are supplementary then their sum is 180 degrees. Deductive ReasoningIf a polygon is regular, then all angles in the interior of the polygon are congruent. If a polygon is regular, then all of its sides are congruent.

Why cant these two statements be combined like the last example.Deductive Reasoning