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共回答了24个问题采纳率:87.5% 举报
(1) C=
![](https://img.yulucn.com/upload/f/02/f02070aa3621158a5c2d9f87ea643afd_thumb.jpg)
;(2)最大值为2,此时A=
![](https://img.yulucn.com/upload/3/1a/31a5e8f447e353dba9f4adf99e44c84b_thumb.jpg)
,B=
(1)利用正弦定理化简csinA=acosC.求出tanC=1,得到
![](https://img.yulucn.com/upload/5/47/547562cdcaaed709e7f150a48bc41957_thumb.jpg)
.
(2)
![](https://img.yulucn.com/upload/f/3e/f3e26fb55d746e67d45952162f1c5a3e_thumb.jpg)
,化简
![](https://img.yulucn.com/upload/2/58/258b42c79f51a4d672bb9b01571999d2_thumb.jpg)
sinA-cos
.因为
![](https://img.yulucn.com/upload/f/20/f205cb5ccc9210180fd6e663f282c2da_thumb.jpg)
,推出
![](https://img.yulucn.com/upload/e/74/e7443618addb9baeb62f8735ab036257_thumb.jpg)
,求出
![](https://img.yulucn.com/upload/2/8c/28cf891139a6bb68554b192ec646be1d_thumb.jpg)
取得最大值2.
得到
![](https://img.yulucn.com/upload/f/aa/faac28367dae42f2159b7566705c31f5_thumb.jpg)
,
![](https://img.yulucn.com/upload/3/2d/32d6b95242e326f42d9c5a0f324b084c_thumb.jpg)
.
(1)由正弦定理得sinCsinA=sinAcosC.……(2分)
因为0
0.
从而sinC=cosC.…………………………………………(4分)
又cosC≠0,所以tanC=1,则C=![](https://img.yulucn.com/upload/f/02/f02070aa3621158a5c2d9f87ea643afd_thumb.jpg)
.……………………(5分)
(2)由(1)知,B=
![](https://img.yulucn.com/upload/0/bf/0bfd15331629918c901ab7da51c48a00_thumb.jpg)
-A,于是
![](https://img.yulucn.com/upload/2/58/258b42c79f51a4d672bb9b01571999d2_thumb.jpg)
sinA-cos
![](https://img.yulucn.com/upload/c/59/c595a084440e467ff86f9ea64c0b8b0a_thumb.jpg)
=
![](https://img.yulucn.com/upload/2/58/258b42c79f51a4d672bb9b01571999d2_thumb.jpg)
sinA-cos(π-A)……………………(5分)
=
![](https://img.yulucn.com/upload/2/58/258b42c79f51a4d672bb9b01571999d2_thumb.jpg)
sinA+cosA=2sin
![](https://img.yulucn.com/upload/2/cb/2cb45cd7fd25fea15c4c9efc6f46ef4a_thumb.jpg)
.…………………………………(7分)
因为0
![](https://img.yulucn.com/upload/0/bf/0bfd15331629918c901ab7da51c48a00_thumb.jpg)
,所以
![](https://img.yulucn.com/upload/1/55/155531410b244f429a0e4765875d5279_thumb.jpg)
<
![](https://img.yulucn.com/upload/a/fc/afccd2ffe07b70f26463e6e67498cd7e_thumb.jpg)
.从而当A+
![](https://img.yulucn.com/upload/1/55/155531410b244f429a0e4765875d5279_thumb.jpg)
=
![](https://img.yulucn.com/upload/8/80/8808410c2e8fd2f5d2233d095d599c33_thumb.jpg)
,即A=
![](https://img.yulucn.com/upload/3/1a/31a5e8f447e353dba9f4adf99e44c84b_thumb.jpg)
时,
2sin
![](https://img.yulucn.com/upload/2/cb/2cb45cd7fd25fea15c4c9efc6f46ef4a_thumb.jpg)
取最大值2.…………………………………………(9分)
综上,
![](https://img.yulucn.com/upload/2/58/258b42c79f51a4d672bb9b01571999d2_thumb.jpg)
sinA-cos
![](https://img.yulucn.com/upload/c/59/c595a084440e467ff86f9ea64c0b8b0a_thumb.jpg)
的最大值为2,此时A=
![](https://img.yulucn.com/upload/3/1a/31a5e8f447e353dba9f4adf99e44c84b_thumb.jpg)
,B=
![](https://img.yulucn.com/upload/3/51/3511e066e44b3580d1e734830886da66_thumb.jpg)
.……………(10分)
1年前
10