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Multiply rational numbers
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Slide 1

multiply rational numbers.

multiply rational numbers.

SOL: none

Objective The student will be able to:

Designed by Skip Tyler, Varina High School and Nicole Kessinger Deep Run High School

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Slide 2

Multiplying Rules

Multiplying Rules

1) If the numbers have the same signs then the product is positive.

(-7) Х (-4) = 28

2) If the numbers have different signs then the product is negative.

(-7) Х 4 = -28

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Slide 3

Examples

Examples

1) (3x)(-8y)

Write both numbers as a fraction.

Cross-cancel if possible.

Multiplying fractions:

top # Х top #

Bottom # Х bottom#

-24xy

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Slide 4

When multiplying two negative numbers, the product is negative.

When multiplying two negative numbers, the product is negative.

True

False

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Slide 5

When multiplying a negative number and a positive number, use the sign of the larger number.

When multiplying a negative number and a positive number, use the sign of the larger number.

True

False

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Slide 6

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Slide 7

Multiply: (-3)(4)(-2)(-3)

Multiply: (-3)(4)(-2)(-3)

72

-72

36

-36

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Slide 8

an easy way to determine the sign of the answer

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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Slide 9

Positive or negative answer?

Positive or negative answer?

Positive - even # of negative signs (4)

Write all numbers as fractions and multiply.

=12

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Slide 10

What is the sign of the product of (-3)(-4)(-5)(0)(-1)(-6)(-91)?

What is the sign of the product of (-3)(-4)(-5)(0)(-1)(-6)(-91)?

Positive

Negative

Zero

Huh?

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