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)