题目内容
(1+x)+(1+x)2+(1+x)3+…+(1+x)15的展开式中含x3项的系数是______.(用数字作答)
所给式子的展开式中x3的系数是
+
+
+…+
=
+
+
+…+
=
+
+
+…+
=
+
+…+
=…=
+
=
=1820.
故答案为 1820.
| C | 33 |
| C | 34 |
| C | 35 |
| C | 315 |
| C | 44 |
| C | 34 |
| C | 35 |
| C | 315 |
=
| C | 45 |
| C | 35 |
| C | 36 |
| C | 315 |
| C | 46 |
| C | 36 |
| C | 315 |
| C | 415 |
| C | 315 |
| C | 416 |
故答案为 1820.
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