1.4-5: Multiplying Integers: Basic Rules

Ways to Express multiplication

• Remember: All of these mean the same thing:

Five times four 5 × 4 5 · 4 5(4)

Multiplying on a Number Line:Positive Integers

• 5(3)

Multiplying on a Number Line:Positive times Negative

• 5(–3)

• –5(3)

Multiplying on a Number Line:Negative times Negative

• –5(–3)

Rules for Multiplying Integers

• If the signs of the factors are the same, the product is positive:

3(2) = 6 –3(–2) = 6

• If the signs of the factors are different, the product is negative:

–3(2) = –6 3(–2) = –6

Dividing Integers

• Remember, division can be written like this:

32 ÷ 16

...or like this:

Dividing Integers

• To divide integers, follow the same rules as for multiplying:Negative divided by negative has positive result.

Positive divided by negative or negative divided by positive

…has negative result.

IMPORTANT: Division by Zero

• Division by zero is undefined (not defined) in our everyday number system.

• In other words, “3 ÷ 0” has no answer.

• If you are supposed to evaluate an expression such as

–10 ÷ 0You should write this answer: undefined

Try It Yourself

1. 3(8)2. 3(–8)3. –3(–8)4. –3(8)

5. 2(–4)6. –2(–4)7. –2(4)

8. –3(0)9. –10(10)10.0(–15)11.–10(–10)

12.–5(–5)13.–5(5)14.5(–4)