jianghexiang1981
幼苗
共回答了24个问题采纳率:87.5% 举报
(1) 2
10 (2) 1(3) 2
9 (4)
![](https://img.yulucn.com/upload/e/8f/e8fdeab9d097232288471d738b463a75_thumb.jpg)
(5)
设(2x-3y)
10 =a
0 x
10 +a
1 x
9 y+a
2 x
8 y
2 +…+a
10 y
10 (*)
各项系数和即为a
0 +a
1 +…+a
10 ,奇数项系数和为a
0 +a
2 +…+a
10 ,偶数项系数和为a
1 +a
3 +a
5 +…+a
9 ,x的奇次项系数和为a
1 +a
3 +a
5 +…+a
9 ,x的偶次项系数和a
0 +a
2 +a
4 +…+a
10 .
由于(*)是恒等式,故可用“赋值法”求出相关的系数和.
(1)二项式系数和为C
![](https://img.yulucn.com/upload/1/c0/1c05dd0a0bef72569f8993602b0aea36_thumb.jpg)
+C
![](https://img.yulucn.com/upload/6/ad/6ad63f776b675904b58264e83d0d3117_thumb.jpg)
+…+C
![](https://img.yulucn.com/upload/0/a9/0a979676316dbc7f3a400b084525c000_thumb.jpg)
=2
10 .
(2)令x=y=1,各项系数和为(2-3)
10 =(-1)
10 =1.
(3)奇数项的二项式系数和为C
![](https://img.yulucn.com/upload/1/c0/1c05dd0a0bef72569f8993602b0aea36_thumb.jpg)
+C
![](https://img.yulucn.com/upload/c/15/c150f7224a966ff74fe3de1e2acc0660_thumb.jpg)
+…+C
![](https://img.yulucn.com/upload/0/a9/0a979676316dbc7f3a400b084525c000_thumb.jpg)
=2
9 ,
偶数项的二项式系数和为C
![](https://img.yulucn.com/upload/6/ad/6ad63f776b675904b58264e83d0d3117_thumb.jpg)
+C
![](https://img.yulucn.com/upload/e/3d/e3ddff09c51c290cf6b83f6d153e3235_thumb.jpg)
+…+C
![](https://img.yulucn.com/upload/9/8b/98b5aff36ac34439413f495476b400e8_thumb.jpg)
=2
9 .
(4)设(2x-3y)
10 =a
0 x
10 +a
1 x
9 y+a
2 x
8 y
2 +…+a
10 y
10 令x=y=1,得到a
0 +a
1 +a
2 +…+a
10 ="1" ①
令x=1,y=-1(或x=-1,y=1)
得a
0 -a
1 +a
2 -a
3 +…+a
10 =5
10 ②
①+②得2(a
0 +a
2 +…+a
10 )=1+5
10 ,
∴奇数项的系数和为
![](https://img.yulucn.com/upload/1/5d/15d3e924b746d5dc9eb4c9b5d002ad20_thumb.jpg)
;
①-②得2(a
1 +a
3 +…+a
9 )=1-5
10 ,
∴偶数项的系数和为
![](https://img.yulucn.com/upload/e/8f/e8fdeab9d097232288471d738b463a75_thumb.jpg)
.
(5)x的奇次项系数和为a
1 +a
3 +a
5 +…+a
9 =
![](https://img.yulucn.com/upload/e/8f/e8fdeab9d097232288471d738b463a75_thumb.jpg)
;
x的偶次项系数和为a
0 +a
2 +a
4 +…+a
10 =
![](https://img.yulucn.com/upload/1/5d/15d3e924b746d5dc9eb4c9b5d002ad20_thumb.jpg)
.
1年前
2