| 5 |
| 6 |
| 7 |
| 12 |
| 9 |
| 20 |
| 11 |
| 30 |
| 13 |
| 42 |
| 15 |
| 56 |
| 17 |
| 72 |
| 19 |
| 90 |
=1-（
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 4 |
| 1 |
| 5 |
| 1 |
| 5 |
| 1 |
| 6 |
| 1 |
| 6 |
| 1 |
| 7 |
| 1 |
| 7 |
| 1 |
| 8 |
| 1 |
| 8 |
| 1 |
| 9 |
| 1 |
| 9 |
| 1 |
| 10 |
=1-
| 1 |
| 2 |
| 1 |
| 10 |
=
| 1 |
| 2 |
| 1 |
| 10 |
=
| 3 |
| 5 |
故答案为：
| 3 |
| 5 |
1−5/6+7/12−9/20+11/30−13/42+15/56−17/72+19/90=_．
1−
+
−
+
−
+
−
+
=______．
| 5 |
| 6 |
| 7 |
| 12 |
| 9 |
| 20 |
| 11 |
| 30 |
| 13 |
| 42 |
| 15 |
| 56 |
| 17 |
| 72 |
| 19 |
| 90 |
数学人气：122 ℃时间：2019-08-17 13:50:50
优质解答
1-
+
-
+
-
+
−
+
，
=1-（
+
）+（
+
）-（
+
）+（
+
）+（
+
）-（
+
）+（
+
）-（
−
），
=1-
+
，
=
+
，
=
．
故答案为：
．
=1-（
=1-
=
=
故答案为：
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