设 与 复合而得到函数 .若在点可导, 对具有连续偏导数, 则复合函数 在点可导, 且 。（ ）http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/9407bba37a6e4e34826276c13978a22a.png

内压球形容器的应力为： A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/7a7e20156c8c4502840fc258ffe21c74.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/6b137ba6e7464b2c8122eced2a3d45cd.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/3c032f5116a04b288400df17925e39c2.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/85ca21668f4045e2b864897bc3795fdf.png">

若偏导数http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/a1b21fe4866c4a31bc3d618a2ea3c815.png存在，则http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/7cb9e1dd6acf40e6abfc4d2b731eeef2.png在点http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/e1a9c8e68bfc4a8f949807cf6c5f0a12.png处连续。<span style="font-family: 宋体;</span><br><br>

设区域，则的值为。( ）http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/468d5951e23a436ba9cd1954573d5aef.png

http://image.zhihuishu.com/zhs/onlineexam/ueditor/201803/75f92f05d558450f9e68e52200633e6b.png