题干
用简便方法计算：
（1+
+
+
）×（
+
+
+
）-（1+
+
+
+
）×（
+
+
）= ____
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 6 |
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 6 |
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 4 |
答案(点此获取答案解析）
| 1 |
| 6 |
