Multiply and rational numbers Objective The student will be able to:
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Transcript of Multiply and rational numbers Objective The student will be able to:
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Multiply and rational numbers
ObjectiveThe student will be able to:
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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
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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
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When multiplying two negative numbers, the product is negative.
1. True2. False
Answer Now
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When multiplying a negative number and a positive number, use the sign of
the larger number.1. True2. False
Answer Now
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25
58
3)
1040
=
14
=
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Multiply: (-3)(4)(-2)(-3)1. 722. -723. 364. -36
Answer Now
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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?
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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
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What is the sign of the product of (-3)(-4)(-5)(0)(-1)(-6)(-91)?
1. Positive2. Negative3. Zero4. Huh?
Answer Now
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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
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When dividing two negative numbers, the quotient is positive.
1. True2. False
Answer Now
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When dividing a negative number and a positive number, use the sign of the
larger number.1. True2. False
Answer Now
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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.
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Example #1
72
.27
The reciprocal of is
27
72
11
1
Example #2The reciprocal of -3 is
13
.11
131
13
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Basically, you are flipping the fraction!
We will use the multiplicative inverses for dividing fractions.
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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
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When dividing fractions, change division to multiplying by the reciprocal.
Examples1)
34
58
34
85
65
2420
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2) 15
3
10
15
103
1015
23
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What is the quotient of-21 ÷ -3?
1. 182. -183. 74. -7
Answer Now
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1 10 ?5 3
Answer Now
23
233
503
50
1. .
2. .
3. .
4. .