#### Math - 2018-19

# G.1 - Logic and Proofs

G.1The student willusedeductive reasoning toconstructandjudgethe validity of a logical argument consisting of a set of premises and a conclusion. This will includea)

identifyingthe converse, inverse, and contrapositive of a conditional statement;b)

translatinga short verbal argument into symbolic form;c)

determiningthe validity of a logical argument.

*Adopted: 2016*

### BIG IDEAS

- I can analyze the logic behind advertising, decide the official weight
of a Hershey bar by weighing a fraction of the candy bars coming off a
production line, and present a winning a court case.

- I will develop
logical critical thinking by drawing conclusions and making inferences from
known or assumed facts.

### UNDERSTANDING THE STANDARD

· Inductive reasoning, deductive reasoning, and proof are critical in establishing general claims.

· Deductive reasoning is the method that uses logic to draw conclusions based on definitions, postulates, and theorems.

· Valid forms of deductive reasoning include the law of syllogism, the law of contrapositive, the law of detachment, and the identification of a counterexample.

· Symbolic notation is used to represent logical arguments, including the use of , , , , , and .

· The law of syllogism states that
if *p** q* is true and *q ** r* is true, then

*p **r* is true.

· The law of contrapositive states
that if *p** q* is true and *q* is true, then *p* is true.

· The law of detachment states that
if *p** q* is true and *p* is true,
then

*q* is true.

· A counterexample is used to show an argument is false.

· Inductive reasoning is the method of drawing conclusions from a limited set of observations.

· Proof is a justification that is logically valid and based on initial assumptions, definitions, postulates, theorems, and/or properties.

· Logical arguments consist of a set of premises or hypotheses and a conclusion.

· When a conditional (*p** q*) and its converse (*q** p*) are true, the statements can be written as a biconditional, *p* *iff*
*q*; or* p if and only if q*;or* p ** q*.

· Logical arguments that are valid may not be true. Truth and validity are not synonymous.

· Exploration of the representation of conditional statements using Venn diagrams may assist in deepening student understanding.

· Formal proofs utilize symbols of formal logic to determine validity of a logical argument.### ESSENTIALS

**The student will use problem solving, mathematical communication, mathematical reasoning, connections, and representations to**

· G.1a_{1} **Identify**
the converse, inverse, and contrapositive of a conditional statement.

· G.1b_{1} **Translate**
verbal arguments into symbolic form using the symbols of formal logic.

· G.1c_{1} **Determine**
the validity of a logical argument using valid forms of deductive reasoning.

· G.1c_{2} **Determine**
that an argument is false using a counterexample.

### KEY VOCABULARY

conditional
statement, converse, inverse, contrapositive, verbal argument,
hypothesis/premises, conclusion, symbolic form, deductive reasoning, inductive reasoning, law of syllogism, law of
contrapositive, law of detachment, counterexample, proof, Venn diagram ,
intersections, unions, negation, therefore,
compound, conjunction, disjunction, conjecture, truth value, validity,
truth table, biconditional, postulates/axioms, theorems, Euclidean geometry,
axiomatic system, undefined terms, point, line, plane, algebraic properties

*Updated: Aug 23, 2018*