"Multiplication of Rational Numbers" PPT courseware

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"Multiplication of Rational Numbers" PPT courseware

4 × 7 = 28

3 × 0 = 0

5 × 2 × 7 = 70

6 × 9 × 0 × 4 = 0

(-3)×2=? (-3)×(-2)=?

think about it

2×3=6 (–2)×3= – 6

2×(–3)= – 6 (–2)×(–3)=6

When two numbers are multiplied together, if they have the same sign, they get ____, if they have different signs, they get ____, and when they multiply their absolute values;

0 multiplied by any number gives ____.

Use your brain: Can you calculate the multiplication of several rational numbers?

2×3×4× (-5)=_____

2×3×(-4)×(-5)=_____

2×(-3)×(-4) ×(-5)=_____

(-2)×(-3)×(-4)×(-5)=_____

We know by observation

When several numbers other than 0 are multiplied together and the number of negative factors is an even number, the product is a positive number;

When the number of negative factors is odd, the product is negative.

Example 3 Calculation:

(1) (-5) × 8 × (- 7) × (- 0.25)

(2) 7.8×(-8.1)×0×(-19.6)

Solution: (1) Original formula = - (5×8×7×0.25) = - 70

(2) Original formula = 7.8×8.1×0×19.6 = 0

Little discovery:

When several numbers are multiplied together, if any of the factors is 0, the product equals ____.

Class summary

Rational multiplication rule

When two numbers are multiplied together, the numbers with the same sign are positive, the numbers with different signs are negative, and the absolute values ​​are multiplied together.

When any number is multiplied by 0, the product is still 0.

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Update Time: 2024-09-11

This template belongs to Mathematics courseware Hebei Education Edition Seventh Grade Mathematics Volume 1 industry PPT template

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