Geometry Chapter 2
Conditionals A conditional is a statement that can be written in the If – Then form. If the team wins the semi-final, then it will play in the championship.
Conditionals The “If” part is called the Hypothesis. If the team wins the semi-final, then it will play in the championship. The “Then” part is called the Conclusion.
Hypothesis Conclusion Conditionals Hypothesis Conclusion p q When If Then All verbs Then Subject adjectives If are...
If Hypothesis Then Conclusion Conditionals Conditional If Hypothesis Then Conclusion p q Converse If Then Conclusion Hypothesis Hypothesis Conclusion q p
Conditionals p q If the team wins the semi-final, then it will play in the championship. q p Converse If the team plays in the championship, then it won the semi-final. If it will play in the championship, then the team wins the semi-final.
Conditionals p q q p ~ p ~ q ~ q ~ p Conditional If the team wins the semi-final, then it will play in the championship. p q Converse If the team plays in the championship, then it won the semi-final. q p If the team does not win the semi-final, then it will not play in the championship. Inverse ~ p ~ q Contrapositive If the team does not play in the championship, then it did not win the semi-final. ~ q ~ p
True False it could be a lion False it could be a lion True All tigers are cats. Conditional If an animal is a tiger, then it is a cat. True p q False Converse If an animal is a cat, then it is a tiger. it could be a lion q p False Inverse If an animal is not a tiger, then it is not a cat. it could be a lion ~ p ~ q Contrapositive If an animal is not a cat, then it is not a tiger. True ~ q ~ p
Postulates Through any two points there exists exactly one line. If two points exist, then exactly one line passes through them.
Postulates A line contains at least two points. If a line exists, then it contains at least two points.
Postulates If two lines intersect, then their intersection is exactly one point.
Postulates Through any three noncollinear points there exists exactly one plane. If three noncollinear points exist, then exactly one plane contains them.
Postulates A plane contains at least three noncollinear points. If a plane exists, then it contains at least three noncollinear points.
Postulates If two points lie in a plane, then the line containing them lies in the plane.
Postulates If two planes intersect, then their intersection is a line.
Biconditionals True True p q q p p q Conditional If an angle is acute, then it has a measure less than 90. p q Converse If an angle has a measure less than 90, then it is an acute angle. True q p If both the conditional and its Converse are true, then it can Be written as a biconditional. Biconditional p q “if and only if” An angle is acute if and only if It has a measure less than 90.
Practice http://www.glencoe.com/sec/math/studytools/cgi-bin/msgQuiz.php4?isbn=0-02-834817-6&chapter=1&lesson=4
Notice how the original Conditional has been Law of Detachment (1) p q Notice how the original Conditional has been Broken apart into two pieces. (Detached) (2) p (3) q
Law of Detachment p q p q If you pass the driving test, then you will get your license. p Brian passed his driving test. q Brian got his license.
(1) p q (2) q r (3) p r Law of Syllogism Notice how all three statements are conditionals with three basic ideas. The repeating part cancels out to give the conclusion. (2) q r (3) p r
Law of Syllogism p q q r p r If you pass the driving test, then you will get your license. q r If you get your license, then you can drive to school. p r If you pass the driving test, then you can drive to school.
If it is not a conditional and not a p statement, Then there is Working the Laws If it is not a conditional and not a p statement, Then there is NO CONCLUSION! Identify the p and q If no, is it a p? Then check for Detachment. If yes, check for syllogism. Is 2nd statement another conditional ?
3- Joe Nathan has an ID number. Law of Detachment Examples: 1- If a student is enrolled at Lyons High, then the student has an ID number. p q p: student enrolled @Lyons High q: student has an ID number 2- Joe Nathan is enrolled at Lyons High. p 3- Joe Nathan has an ID number. q Law of Detachment
NO CONCLUSION Examples: 1- If your car needs more power, use Powerpack Motor Oil. p q p: car needs more power q: use Powerpack Motor Oil q 2- Marcus uses Powerpack Motor Oil. NO CONCLUSION
3- If fossil fuels are burned, then wildlife suffers. Law of Syllogism Examples: 1- If fossil fuels are burned, then acid rain is produced. p q p: fossil fuels are burned q: acid rain is produced. q r 2- If acid rain falls, wildlife suffers. 3- If fossil fuels are burned, then wildlife suffers. p r Law of Syllogism
INVALID Examples: 1- If a rectangle has four congruent sides, then it is a square. p q p: a rectangle has four congruent sides q: it is a square 2- A square has diagonals that are perpendicular. q r 3- If a rectangle has four congruent sides, then its diagonals are perpendicular. 3- A rectangle has diagonals that are perpendicular. INVALID