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Examples 1) (3x)(-8y) 2) Write both numbers as a fraction. Cross-cancel if possible. =-16 Multiplying fractions: top # Bottom # bottom# -24xy
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Multiply and rational numbers
ObjectiveThe student will be able to:
Multiplying Rules
1) If the numbers have the same signs then the product is positive.
(-7) • (-4) = 282) If the numbers have different
signs then the product is negative.(-7) • 4 = -28
Examples
1) (3x)(-8y)
20 45
2) Write both numbers as a fraction.
Cross-cancel if possible.
201
45
805
= -16
Multiplying fractions:
top # • top #
Bottom # • bottom#
-24xy
When multiplying two negative numbers, the product is negative.
1. True2. False
Answer Now
When multiplying a negative number and a positive number, use the sign of
the larger number.1. True2. False
Answer Now
25
58
3)
1040
=
14
=
Multiply: (-3)(4)(-2)(-3)1. 722. -723. 364. -36
Answer Now
an easy way to determine the sign of the answer
3 negative signs -> Odd -> answer is negative-480
When you have an odd number of negatives, the answer is negative.
When you have an even number of negatives, the answer is positive.
4) (-2)(-8)(3)(-10)Do you have an even or odd number of
negative signs?
Last one!
5) 12
6 5 2
5
2
Positive or negative answer?Positive - even # of negative signs (4)
Write all numbers as fractions and multiply.
=12
12
61
51
25
21
12010
What is the sign of the product of (-3)(-4)(-5)(0)(-1)(-6)(-91)?
1. Positive2. Negative3. Zero4. Huh?
Answer Now
Dividing Rules
1) If the numbers have the same signs then the quotient is positive.
-32 ÷ (-8 )= 42) If the numbers have different
signs then the quotient is negative.81 ÷ (-9) = -9
When dividing two negative numbers, the quotient is positive.
1. True2. False
Answer Now
When dividing a negative number and a positive number, use the sign of the
larger number.1. True2. False
Answer Now
The reciprocal of is
where a and b 0.
ab
ba
The reciprocal of a number is called its multiplicative inverse.
A number multiplied by its reciprocal/multiplicative inverse is
ALWAYS equal to 1.
Example #1
72
.27
The reciprocal of is
27
72
11
1
Example #2The reciprocal of -3 is
13
.11
131
13
Basically, you are flipping the fraction!
We will use the multiplicative inverses for dividing fractions.
Which statement is false about reciprocals?
1. Reciprocals are also called additive inverses
2. A number and its reciprocal have same signs
3. If you flip a number, you get the reciprocal
4. The product of a number and its reciprocal is 1
Answer Now
When dividing fractions, change division to multiplying by the reciprocal.
Examples1)
34
58
34
85
65
2420
2) 15
3
10
15
103
1015
23
What is the quotient of-21 ÷ -3?
1. 182. -183. 74. -7
Answer Now
1 10 ?5 3
Answer Now
23
233
503
50
1. .
2. .
3. .
4. .
