Ch 1.6 Commutative & Associative Properties Objective: To understand the difference between the Commutative and Associative Properties
Definitions a + b = b + a 3 + 5 = 5 + 3 4 7 = 7 4 Commute (travel) Commutative Property of Addition a + b = b + a a “travels” to the other side of b 3 + 5 = 5 + 3 Example: Commutative Property of Multiplication a “travels” to the other side of b 4 7 = 7 4 Example:
Are the following operations commutative? 1) Subtraction Counterexamples a - b = b - a 2 - 0 = 0 - 2 2 = -2 Therefore, subtraction is not commutative. 2) Division Therefore, division is not commutative. Counterexample - a single example that proves a statement false.
Examples 2) 8 + 7 = 7 + 8 1) 3 + 1 = 1 + 3 4) 4 9 = 9 4 3) 2 7 = Apply the commutative property 2) 8 + 7 = 7 + 8 1) 3 + 1 = 1 + 3 4) 4 9 = 9 4 3) 2 7 = 7 2 5) 5 + (2 6) = (2 6) + 5 6) (3 + 4) 7 = 7 (3 + 4)
Classwork 7 + 4 = 5 + 6 = 3 8 = 9 2 = (1 + 4) 6 = (2 + 6) 3 = Apply the commutative property 1) 7 + 4 = 2) 5 + 6 = 3) 3 8 = 4) 9 2 = 5) (1 + 4) 6 = 6) (2 + 6) 3 = 1 + (5 7) = 7) 8 + (7 4) = 8) 9) 5 (4 + 6) = 10) (2 2) + 3 =
Definitions ( a + b ) + c = a + ( b + c ) (4 + 11) + 6 = 4 + (11 + 6) Associate (partner) Associative Property of Addition Parenthesis change “partners” – only the parenthesis move ( a + b ) + c = a + ( b + c ) (4 + 11) + 6 = 4 + (11 + 6) Example: Associative Property of Multiplication Parenthesis change “partners” – only the parenthesis move Example:
Are the following operations associative? 1) Subtraction (a - b) - c = a - (b - c) (10 - 5) - 2 = 10 - (5 - 2) Therefore, subtraction is not associative. 5 - 2 = 10 - 3 3 = 7 2) Division Therefore, division is not associative.
Examples 1) 5 + (5 + 7) = ( ) 5 + 5 + 7 6 4 5 ( ) 2) (6 4) 5 = Apply the associative property 1) 5 + (5 + 7) = ( ) 5 + 5 + 7 6 4 5 ( ) 2) (6 4) 5 = 3) (9 + 2) + 8 = 9 + 2 + 8 ( ) 4) 5 (2 9) = ( ) 5 2 9
Classwork (3 + 4) + 1 = (9 + 4) + 6 = (3 4) 5 = (9 2) 10 = Apply the associative property 1) (3 + 4) + 1 = 2) (9 + 4) + 6 = 3) (3 4) 5 = 4) (9 2) 10 = 5) 4 + (1 + 6) = 6) 3 + (2 + 6) = 2 (5 7) = 7) 8 (7 4) = 8) 9) 4 + (6 + 5) = 10) (3 2) 2 =
Commutative vs. Associative ( Flip-flop ) Associative ( Re-group ) Flip-flop Re-grouping