Question

（1）先计算下面各题，再看看有什么规律．

1

2

+

1

3

=

1

2

-

1

3

=

1

3

+

1

4

=

1

3

-

1

4

=

1

4

+

1

5

=

1

4

-

1

5

=
（2）根据上面的规律，直接写出下面各题的得数．

1

3

+

1

5

=

1

7

-

1

8

=

1

2

+

1

7

=

1

3

-

1

7

=

1

8

+

1

5

=

1

4

-

1

9

=

Answer 1

1

2

+

1

3

=

5

6

1

2

-

1

3

=

1

6

1

3

+

1

4

=

7

12

1

3

-

1

4

=

1

12

1

4

+

1

5

=

9

20

1

4

-

1

5

=

1

20

我发现：分子是1，分母是互质数的两个分数相加减，分母的乘积作为分母，分母相加减作为分子．
（2）

1

3

+

1

5

=

8

15

1

7

-

1

8

=

1

56

1

2

+

1

7

=

9

14

1

3

-

1

7

=

4

21

1

8

+

1

5

=

13

40

1

4

-

1

9

=

5

36

．