# 2. ７ 有理数的减法 - PowerPoint PPT Presentation

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2. ７ 有理数的减法

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2.７ 有理数的减法

1、(-5)+(-3)=

2、(-5)+(+3)=

3、(-5)+(+5)=

4、(-5)+ 0 =

8

-

（同号两数相加，取相同的正负号，并把绝对值相加.）

2

-

（绝对值不等的异号两数相加，取绝对值较大的加数的正负号，并用较大的绝对值减去较小的绝对值.）

0

（互为相反数的两个数相加得零.）

-5

（一个数与零相加，仍得这个数.）

1.( )+(-3)=-8;

2.(-8)+( )=-5.

-5

+3

8844-(-155)

( ? )+(-3)=-8.

(-5)+(-3)=-8，

(-8)-(-3)=-5. ①

(-8)-(-3)=-5. ①

(-8)+( )=-5. ②

+3

(-8)-(-3)=(-8)+(+3)

(-5)+(-3)=-8

(-8)-(-3)=-5

(-8)+(+3)=-5

10-6=(___)， 10+(-6)=(___)

4

4

10-6=10+(-6)=4

1. 下列括号内各应填什么数?

(1)(+2)-(-3)=(+2)+( );

(2)0-(-4)=0+( );

(3)(-6)-3=(-6)+( );

(4)1-(+39)=1+( ).

+3

+4

-3

-39

（1）（-32）-（+5）;

（2） 7.3-（-6.8）;

（3）（-2）-（-25）;

（4） 12 - 21.

(1)(-32)-(+5)

-37

=(-32)+(-5)=

=7.3+6.8

=14.1

(2)7.3-(-6.8)

(3)(-2)-(-25)

=(-2)+25

=23

(4)12-21

=12+(-21)

=-9

2. 计算：

(1)(+3)-(-2); (2)(-1)-(+2);

(3)0-(-3); (4)1-5;

(5)(-23)-(-12); (6)(-1.3)-2.6.

3. 填空：

(1)温度3℃比-8℃高;

(2)温度-9℃比-1℃低;

(3)海拔高度-20m比-30m高;

(4)从海拔22m到-10m，下降了.

11 ℃

8℃

10m

32m

### 小结:

1.有理数减法法则:

2.减法转化成加法时应注意:

① P36—37

1、2、4、5（交）

②课课练P27—28

4. 计算：

(1)4.8-(+2.3); (2)(-1.24)-(+4.76);

(3)(-3.28)-1; (4)

(5)

(6)