问题 解答题
1
2
-
1
6
-
1
12
-
1
20
-
1
30
-
1
42
=______.
答案

1
2
-
1
6
-
1
12
-
1
20
-
1
30
-
1
42

=

1
1×2
-
1
2×3
-
1
3×4
-
1
4×5
-
1
5×6
-
1
6×7

=(1-

1
2
)-(
1
2
-
1
3
)-(
1
3
-
1
4
)-(
1
4
-
1
5
)-(
1
5
-
1
6
)-(
1
6
-
1
7
),

=1-

1
2
-
1
2
+
1
3
-
1
3
+
1
4
-
1
4
+
1
5
-
1
5
+
1
6
-
1
6
+
1
7

=

1
7

故答案为:

1
7

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单项选择题