2.1 conditional statements
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Transcript of 2.1 conditional statements
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2.1 Conditional Statements2.1 Conditional Statements
Mrs. StelterGeometryFall 2010
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Standards/Objectives:
Students will learn and apply geometric concepts.
Objectives:Recognize and analyze a conditional
statementWrite postulates about points, lines, and
planes using conditional statements.
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Conditional StatementConditional Statement
A logical statement with 2 parts2 parts are called the hypothesis &
conclusionCan be written in “if-then” form; such as,
“If…, then…”
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Conditional StatementConditional Statement
Hypothesis is the part after the word “If”Conclusion is the part after the word
“then”
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Ex: Underline the hypothesis & circle the conclusion.
If you are a brunette, then you have brown hair.
hypothesis conclusion
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Ex: Rewrite the statement in “if-then” form
1. Vertical angles are congruent.
If there are 2 vertical angles, then they are congruent.
If 2 angles are vertical, then they are congruent.
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Ex: Rewrite the statement in “if-then” form
2. An object weighs one ton if it weighs 2000 lbs.
If an object weighs 2000 lbs, then it weighs one ton.
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CounterexampleCounterexample
Used to show a conditional statement is false.
It must keep the hypothesis true, but It must keep the hypothesis true, but the conclusion false!the conclusion false!
It must keep the hypothesis true, but It must keep the hypothesis true, but the conclusion false!the conclusion false!
It must keep the hypothesis true, but It must keep the hypothesis true, but the conclusion false!the conclusion false!
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Ex: Find a counterexample to prove the statement is false.
If x2=81, then x must equal 9.
counterexample: x could be -9
because (-9)2=81, but x≠9.
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Venn Diagrams
Dogs
labs
If it is a lab, then it is a dog
Michigan
Detroit
If you live in Detroit, then you live in Michigan
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NegationNegation
Writing the opposite of a statement.
Ex: negate x=3
x≠3Ex: negate t>5
t 5
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ConverseConverse
Switch the hypothesis & conclusion parts of a conditional statement.
Ex: Write the converse of “If you are a brunette, then you have brown hair.”
If you have brown hair, then you are a brunette.
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InverseInverse
Negate the hypothesis & conclusion of a conditional statement.
Ex: Write the inverse of “If you are a brunette, then you have brown hair.”
If you are not a brunette, then you do not have brown hair.
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ContrapositiveContrapositive
Negate, then switch the hypothesis & conclusion of a conditional statement.
Ex: Write the contrapositive of “If you are a brunette, then you have brown hair.”
If you do not have brown hair, then you are not a brunette.
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The original conditional statement & its contrapositive will always have the same meaning.
The converse & inverse of a conditional statement will always have the same meaning.
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Assignment:
Pp. 83 (2-34)Pp. 85 (54-58)