MULTIPLICATION OF INTEGERS

Pre requisite knowledge 1.concept of integers

2.concept of representation of integers on number line.

3.concept of addition and subtraction of integers.

4.concept of multiplication of two whole numbers.

Teaching points 1.while multiplying a positive integer and a negative integer,we multiply them as whole

numbers and put a minus sign before the product . We thus get a negative integer

2. The product of two negative integers is a positive integer.we multiply the two negative

integers as whole numbers and put the positive sign before the product.

Continued 3. If the number of negative integers in a

product is even, then the product is a positive integer. If the number of negative integers in a product is odd, then the product is a negative

integer.

Product of two in tegers

by activity method.

Instructional objectives To enable students to know that multiplication of

integers is repeated addition

2.to enable students to know that multiplication of two positive integers through patterns.

3.to enable students to multiply two negative integers.

4.to enable students to find the product of theree or more negative integers

5.to enable students to find the product of two integers by activity method.

Multiplication of positive and negative integers

Multiplication of wholenumbers is repeated addition

5+5+5=3x5=15

Addition of integers can be represented in the same way

(-5)+(-5)+(-5)=-15=3x(-5)

0-5-10-15-20

Find (-3)x5 through the following pattern

3x5=15

2x5=10=(15-5)

1x5=5=(10-5)

0x5=5-5=0

-1x5=0-5=-5

-2x5=-5-5=-10

-3x5=-10-5=-15

We already have 3x(-5)=-15

So we get (-3)x5=-15=3x(-5)

While multiplying a positive integer and a negative integer,we multiply them as wholenumbers and put a minus sign before the product.we thus get a negative

integer

Continued We already have 3x(-5)= -15

So we get (-3)x5 = -15 = 3x(-5)

While multiplying a positive integer and a negative integer,we multiply them as whole

numbers and put a minus sign before the product. We thus get a negative integer .

Multiplication of two negative integers.

Observe the pattern for (-3)x(-2)

(-3)x4=-12

(-3)x3=-12-(-3)= -12+3= -9

(-3)x2=(-9)-(-3)-9+3= -6

(-3)x1=(-6)-(-3)=-3

(-3)x0= -3-(-3)=0

(-3)x -1=0-(-3)=3

(-3)x(-2)=3-(-3)=6

Continuedfrom the pattern , we observe

(-3)x(-1)=3=3x1(-3)x(-2)=6= 3x2

the product of two negative integers is a positive integer.We multiply the two negative integers as whole numbers and put the positive

sign before the product

Product of three or more negative integers

(-4)x(-3)=12

(-4)x(-3)x(-2)=[(-4)x(-3)]x(-2)=12x(-2)=

-24

(-4)x(-3)x(-2)x(-1)=[(-4)x(-3)x(-2)]x(-1)

=(-24)x(-1)

Continued If the number of negative integers in a

product is even , then the product is a positive integer . If the number of negative integers in

a product is odd, then the product is a negative integer.

Materials required for the activity

1.chart paper

2.pencil

3.sketch pens

4.scale

Two find the product of two integers by activity method

0-1-2-3-4-5 1 2 3 4 5

00-1-1-2-2-3-3-4-4 -5-5 11 22 33 44 55

Activity continued

00

00

-1-1

--11

--11--11

-1-1

-1-1

-2-2

-2-2

-3-3

-3-3

1122

33

11 22 33

-4-4

--44-4-4 44

44

P(2)P(2)

Activity continued

00

00

-1-1--22

-2-2-3-3-4-41111

2233 44

-1-1-- -2-2-3-311 33 4455 66

P(-2)P(-2)

11 22 334466

Home Assignment

• 1.find (-31)x(-100).

• 2.find (-45)x18

• 3.find 70x(-19)

• 4.find (-18)x(-5)x(-4)

• 5.find (-3)x(-6)x(-2)x(-1)