2 4mult pos by neg
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TRANSCRIPT
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Multiplication of Integers
Chapter 2.4
Algebra I
Pg 73-77
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Warm-Up
3.8 4.1 3 1
5 6
6.8 0.4
1 1
10 4
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Warm-Up answers
3.8 4.1 15.58 3 1 3 1
5 6 30 10
6.8 0.4 17
1 1 1 4
10 4 10 1
4 2
10 5
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What’s the Deal?
In today’s lesson we will review multiplication and division of signed numbers.
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What and why?
7 x -5 = - 35
+7 x +5 = +35
-7 x 5 = - 35
-7 x -5 = + 35
Multiplication is fast adding.
-5 + -5 + -5 + -5 + -5 + -5 + -5 = -35
5 + 5 + 5 + 5 + 5 + 5 + 5 = 35
-7 + -7 + -7 + -7 + -7 = - 35
- (-7 + -7 + -7 + -7 + -7) = - (-35)
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Count the Negatives
7 x -5 = - 35+7 x +5 = +35-7 x 5 = - 35
-7 x -5 = + 35
Count the negative signs..Ask Odd or Even?
• Odd?Negative
Answer
• Even?Positive
Answer
This works the same for division.
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Number Families
Factor x Factor = Product
F x F = P
Product / Factor = Factor
P / F = F
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Number Families
-8 * 5 = -40
-5 * 8 = -40
-40 / 5 = -8
-40 / 8 = -5
-8 * -5 = 40
-5 * -8 = 40
40 / -5 = -8
40 / -8 = -5
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Try Some
-11 * +5 =
-7 * -10 =
+6 * -5 =
-7 * +8 =
-35 / -5 =+63 / -9 =-56 / -7 =+32 / -8 =
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Try Some - answers
-11 * +5 = - 55
-7 * -10 = + 70
+6 * -5 = - 30-7 * +8 = - 56
-35 / -5 = +7+63 / -9 = -7-56 / -7 = +8+32 / -8 = -4
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Part Two
Fractions and Reciprocals
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Multiply fractions
3 1
5 6
2 1
7 3
7 12
8 23
2
21
1
2
1
10
3
2
21
46
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Reciprocals are used for dividing fractions.
What’s a reciprocal?
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Multiply a number by its reciprocal to get an answer of +1
2
33
2 6
16
What’s the reciprocal of
7/8?
8/7
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Using Reciprocals
• Reciprocals are useful for dividing fractions.
• Rewrite the division of a fraction using multiplication by the reciprocal of the 2nd number.
1 1
3 2
1 1 1 2
3 2 3 1
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Rewrite these number sentences.
4 2
5 7
296
3
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Rewritten number sentences
4 2 4 7 28 14
5 7 5 2 10 5
2 96 396 144
3 1 2
One is your friend.Use 1 to make whole numbers
into fractions.
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