对于图示四种横截面直杆受扭时，适用公式 的截面有四种答案：（注：除(D)外其余为空心截面）正确答案是： A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/6fd10b50fd4646298589880bd489a885.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/dfafbfc5d28943ad9d10675a7d93fe7d.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/fe0a02554480425c89a36003802dd1f9.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/03ce90c73f354ee7a5a51757a450f306.png" />

<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/2205d9f03e724a04b34f2f1045309079.png" />的幅频响应是，幅频响应是。 A: 1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/760d7fcc2f264ed1b10fb836cb48f565.png" /> B: -1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/21f685d2962e4b6993bfcaa513bdbf68.png" /> C: 2，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/57267e995f86426899ce3cc0177a2343.png" /> D: 1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/ea8ba62853a94a15a5620c5165e3594a.png" />

<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/461a52e97ba0474c86bb98b1605911fb.png" />，利用龙贝格算法，求得<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/a84d008c92f542fdb10c225e1dacfc24.png" />_________。 A: 3.06 B: 3.04 C: 3.03 D: 3.015

下列微分方程中常微分方程的是( ) A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/c24b125c0b534b7696bf33f1e7b98c4c.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/2c9f694c97e9426596d13bed4bd474da.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/7ee1366ebe7a40aa868a143ba15c6ed0.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/d46e4fa33ea0443a938c267c2f07c6b4.png">

已知<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/43114282e941476ba93775909fb3f237.png"/>，用拉氏变换法求解微分方程<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/0db291610cb64fa8ad46ae0bd15476b0.png"/> 的结果为（ ） A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/29ff68f02bdd438bb2e16c2a6e1ec18b.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/0010c1593c9145a4b928548ab38cf426.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/1f562f2536584121b53c30e4db08df88.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/f593399cb630435192baa8b3e871b533.png"/>