露华沉香
幼苗
共回答了18个问题采纳率:100% 举报
(I)
![](https://img.yulucn.com/upload/d/25/d25ab556bcda97413f864d724bee2f9d_thumb.jpg)
(II)
![](https://img.yulucn.com/upload/4/f0/4f032e5e41a856c7588dc4d9fe2cb25f_thumb.jpg)
(3)
:
![](https://img.yulucn.com/upload/7/9d/79d9c93a8a53b68dd85cc0edb0ed217a_thumb.jpg)
…2分
![](https://img.yulucn.com/upload/a/ca/acafaf0199a1d49c84b9d7a2475bb353_thumb.jpg)
相减,得x
![](https://img.yulucn.com/upload/1/d5/1d5ade71d3dbca5fc7f35bd705cbb03e_thumb.jpg)
-x
![](https://img.yulucn.com/upload/7/21/721d4bd452d2f2d456340e8221f552be_thumb.jpg)
=2
∴x
![](https://img.yulucn.com/upload/2/04/2046f9c52366c0230798346f2285d3f5_thumb.jpg)
,x
![](https://img.yulucn.com/upload/6/ac/6ac92d270caa40d25d98a5c9d6a46d61_thumb.jpg)
,x
![](https://img.yulucn.com/upload/d/5e/d5e9402d3ffe728e243bbd116d20b79a_thumb.jpg)
,…,x
![](https://img.yulucn.com/upload/c/e7/ce7e6c3f1763ca3bf4a41162d1855809_thumb.jpg)
,…成等差数列;x
![](https://img.yulucn.com/upload/2/54/2546be2a0153df800b92f73f4e044262_thumb.jpg)
,x
![](https://img.yulucn.com/upload/c/aa/caadc7d2f6da1ebcd9477abf12acbbc7_thumb.jpg)
,x
![](https://img.yulucn.com/upload/3/24/324714e12d9063466f2d3474f44324a3_thumb.jpg)
,…,x
![](https://img.yulucn.com/upload/0/c6/0c6f8a48cc3cfd152310bbec0da8328d_thumb.jpg)
,…成等差数列,4分
∴x
![](https://img.yulucn.com/upload/c/e7/ce7e6c3f1763ca3bf4a41162d1855809_thumb.jpg)
= x
![](https://img.yulucn.com/upload/2/04/2046f9c52366c0230798346f2285d3f5_thumb.jpg)
+(n-1)·2=2n+a-2,x
![](https://img.yulucn.com/upload/0/c6/0c6f8a48cc3cfd152310bbec0da8328d_thumb.jpg)
= x
![](https://img.yulucn.com/upload/2/54/2546be2a0153df800b92f73f4e044262_thumb.jpg)
+(n-1)·2=(2-a)+(n-1)·2="2n-a "
![](https://img.yulucn.com/upload/4/f0/4f032e5e41a856c7588dc4d9fe2cb25f_thumb.jpg)
…7分
(3)当n奇数时,An(n+a-1,0),An+1(n+1-a,0),所以 | AnAn+1 | =2(1-a);
当n是偶数时,An(n-a,0),An+1(n+a,0),所以| AnAn-1 | ="2a " …10分
![](https://img.yulucn.com/upload/6/e0/6e018b8dd014bcda5eb9eb5f8d5ed992_thumb.jpg)
要使等腰三角形AnBnAn+1为直角三角形,必需且只需| AnAn-1 | ="2|" BnCn | .
![](https://img.yulucn.com/upload/a/dd/add084968a1ab258c61d8343f2578b89_thumb.jpg)
![](https://img.yulucn.com/upload/c/21/c21c5eba4ecfd283c49d120035e40171_thumb.jpg)
……14分
![](https://img.yulucn.com/upload/d/2b/d2bf47fea7c42d1f0288310c32599314_thumb.jpg)
…15分
![](https://img.yulucn.com/upload/c/0a/c0a33a005d727c24cfca32d2991b583f_thumb.jpg)
…16分
1年前
10