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关键两点:  1、理解问题中的数量关系,如:和、差、积、商与大、    小、多、少、倍,几分之几等。 PowerPoint PPT Presentation


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回顾:. 列代数式关键所在. 关键两点:  1、理解问题中的数量关系,如:和、差、积、商与大、    小、多、少、倍,几分之几等。. 2. 特别是“平方和(差)”与“和(差)的平方”的区别。. 3 、 弄清问题的运算顺序,一般先读的先写。. 2. 填空。. 设甲数为 x ,乙数为 y ,用代数式表示: ( 1 )甲、乙两数的立方和为 ; ( 2 )甲、乙两数和的立方为 ; ( 3 )甲、乙两数的平方差与甲、乙两数的差 的平方比是 。. x 3 + y 3. ( x + y ) 3.

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关键两点:  1、理解问题中的数量关系,如:和、差、积、商与大、    小、多、少、倍,几分之几等。

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5239350

2.

3


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2.

x y

1

2

3

x 3 + y 3

( x + y ) 3

( x 2 - y 2 ) : ( x - y ) 2


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3.2 .

  • :

    1) ,.

    2) .

    3) .

    : ,.

    : .


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  • ;

6

-3


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1.

2.

3.


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1 . x2-1

(1)x=2 (2)x=1/2

(1)x=2

x2-1= 22-1

= 4-1

= 3

(2)x=1/2

x2-1= (1/2)2-1

= 1/4-1

= -3/4

(1)

(2)


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2 .x=2y=-3x(x-y)

x=2y=-3

x(x-y) = 2[2-(-3)]

=2 5

=10

(1)

(2)


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1.

a=2,b=1

a=1,b=2

2.

3.


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3.

a

10

2


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3.a10%2

a1+10%

a1+10%1+10%

=1.21a

2

1.21a =1.212=2.42

1.21a22.42


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  • 4 . a=4b=-2(1)(a+b)2 (2)(a-b)2

    • (3)a2+b2 (4)a2-b2

(2)a=4b=-2

(a-b)2 = [4-(-2)]2

=6 2

=36

ab

(a+b)2

a2+b2

ab

(a-b)2

a2-b2

(1)a=4b=-2

(a+b)2 = [4+(-2)]2

=2 2

=4

(4)a=4b=-2

a2-b2 = 42- (-2) 2

=16-4

=12

(3)a=4b=-2

a2+b2 = 42+(-2)2

=16+4

=20


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3 .x=2y=-3

x(x-y)

1:

(1)

(2)

(3)

(4)

x=2y=-3

x(x-y)

= 2[2-(-3)]

=2 5

=10

2

(1)

(2)


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1

2

3

400


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1

-2a+1

a

4

-4

0

-2/3

-7

9

0

1

7/3


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2


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3abn

n=6,a=5,b=10

a

n=6,a=5,b=10

n (a+b)/2

= 6(5+10)/2

=45

n=6,a=5,b=1045

n

b


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4

1

2


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5

45


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3.,104 x,,?

x

10


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1.

2.

3.


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