L 2.5 Warm-Up Exercises

FIND THE SUM OF THE MATRICES.

5 7-

2- 4

4 8

2- 3-

2.5 Multiplying Real Numbers

Multiplication RulesObjective: To multiply positives and negatives, including decimals and fractions!!

1. (6)(-4) 2. -4c (5d)

3. (-1)(-12) 4. 12 (-3)

5. - 2 -11 6. (7)(-7)

7. 8 (-3)(2) 8. -2 -6 -4

9. (-3b)(-4b)(-2z)(-5z)(-1)

Does the number of negative values(signs) affect the sign of the product? How?

Same signs “+”Diff. signs “–”Even “-” signs “+”Odd “-” signs “–”

-24 -20cd

-12 -36

22 -49

-48 -48

-120 b2z2

Multiplying Decimals What is the rule for multiplying

decimals?

Try these: Don’t forget the sign!!

10. (2.4)(-3.1) 11. 4.2(1.14) 12. (-5.3)(-0.04)

13. (2.93)(0.012) 14. (-10)(3.56)(-2)

Line up at the right and multiply as whole number, when finished, place decimal point from right for the total number of decimal digits.

-7.44 4.788 0.212

0.03516 71.2

5 Minute Brain Break

USE THIS TIME TO relax and/or STETCH OUT….

Try this Brain Puzzle…

In each sentence, an animal is concealed. The first sentence has dog concealed. Can you find the others?

1. What shall I do, Gertrude?2. Asking nutty questions can be most annoying.3. A gold key is not a common key.4. Horace tries in school to be a very good boy.5. People who drive too fast are likely to be arrested.6. Did I ever tell you, Bill, I once found a dollar?7. John came late to his arithmetic class.8. I enjoy listening to music at night.

Multiplying Fractions

Try these: Don’t forget the sign!!

15. 16. 17.

18. 19.

5

3

3

2

1833

116

43

76

127

21

2553 c3

c245

n6

What is the rule for multiplying fractions?

What should you do to make whole numbers look like

fractions?

Diagonally or vertically cancel the greatest common factor between any numerator and denominate and then multiply the numerators and denominates.

Just put a dummy denominate “1”.

2

51

15

4n3

3

8

Properties of Multiplication

Properties of Multiplication

Definition Example

Commutative a · b = b · a

Associative (a · b) · c = a ·(b · c)

Identity a · 1 = a

4 · (-2) = (-2) · 4

[(-4) · 3] · (-2) = (-4) · [ 3 · (-2)]

(-2) · 1 = -2

Ex. (2) (–x) = –2x 3 (–n)(–n) = 3n2

–(y)4 = –(y·y·y·y) = –y4

Multiplying

NegativeX

Negative

PositiveX

Positve

DecimalsFractions

POSITIVE!

Straight Across

I

Ignore DecimalsCount Numbers

Behind DecimalsTo Figure Out

Where DecimalGoes

Whole Numbers

PositiveX

Negative

NegativeX

Positive

NEGATIVE!

Summary

Daily Homework Quiz

Find the Product.

1.(-2)(8)(-1)2.(7)(-3)(-5)(-1/2)

3. Evaluate a³ + 2a² - a when a = -2

In-Class AssignmentTextbook Pages 96

#’s 16-49 (All)