如题：在一步到达矩阵中，有多少个“∞”：http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/265da6f322b0465cb555d0b0388a2446.png
举一反三
- 要使<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/c4b80714c3b14a559ae5bdcd09ef1fc6.png"/>是线性方程组AX=0的基础解系，则只要系数矩阵A=（ ）. A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/fb16cbefa5a746599e585bcf30dce878.png"/> B: ［2 1 1］ C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/df5d7a834bd44f44a519eaffffd47d39.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5adacc7663b444d69f148ab2e7a11cf1.png"/>
- 在电感元件的交流电路中，已知<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/a818ffec501541eaacdc3fd4b3458bfa.png" />，则（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/70961d125a8a493cbdbd3169e8655336.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/65f4ae24f45041548b04d5bb8c113767.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/20d9ff741d534721b621dfe04fb3b2bd.png" />
- 一定量的理想气体，在温度不变的条件下，当压强降低时，分子的平均碰撞频率<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />和平均自由程<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />的变化情况是（ ）： A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />和<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />都减小． B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />减小而<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />增大． C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />和<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />都增大． D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />增大而<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />减小．
- 如图所示，圆形截面区域内存在着与截面相垂直的磁场，磁感应强度随时间变化．磁场区域外有一与圆形截面共面的矩形导体回路 <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/0eea13cd51b54af3b701a0035e6416fe.png" />，以<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/865048ee310d46e09b743d6cfc93fa4a.png" />表示在导体<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/55379797515a41b88e0dcb947c44b585.png" />段上产生的感生电动势， I 表示回路中的感应电流，则（ ）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/95d31735160f47dcb4d8f5ac973c0ce8.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/986a62c34302465cad899f00080acc4f.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/4b6ab53aeebc4f92b722d8fff6237a87.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/d869de90826645c1b386e2019aa86be2.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/da8edb3a9af0442bb11dcee16f061375.png" />
- 理想气体卡诺循环过程的两条绝热线下的面积大小（图中阴影部分）分别为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/64280a32f9a4401f98f6b6af70e231df.png" />，则二者的大小关系是（ ）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/780b6d8d2ff542618f571d6996cd2cab.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/beb26455791a4b07bce0ac35eba22212.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/4bdc821d2c3946d288266564f445e908.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/08c97c45c5d54526a81db7c2679f8fcf.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/6a476124a610477b9ebf6723989ae08c.png" />