根据瞬时速度矢量的定义，在直角坐标系下，其大小可表示为
A:
B:
C:
D:
A:
B:
C:
D:
举一反三
- 下列函数中为奇函数的是( ) A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/7d0e4f5547744249b8c4c0e6db0e62fc.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/d19abeb7724248dca0a0c1b8017897db.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/3f5cff0b4a9b441da3b9e75bd446c141.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/d59a9db29be640a899356a3f1645a0dd.png">
- 下列化合物能发生Hoffmann重排反应的是（ ） A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/48290165247643e1aac1067c27f0cfce.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/04103b28f4ec4c5f8d28d8f8392e143f.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/80cb1b0a7023476496199ba53a5f28f3.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/72d151e6a82943c6b11abdffa60b68c0.png" />
- 下列化合物中不能发生碘仿反应的是( ) A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/0dff63271c6c4de9b7f03cb96261c5dc.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/4abfad75020f40f89720a58429a59426.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/a2517651d2ba48e5be59131fd9e30a4f.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/4fa29dce98f542d883f395cefd3908df.png" />
- 下列基团中吸电子能力最强的是（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/18902949ac9142beb6b84407debff192.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/c5ceca45d0dc49789321fba46295c6f9.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/d87661c43e124df88ce64fc1c55932b7.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/69c2916d66284096b7c7f1a2a26242da.png" />
- 在四阶行列式的展开式中，下列各项中带正号的是（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/158559e94ae84536851f378e695766bb.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/e8261729bcf04dd7ac6f192652f99b12.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/13225b1635fb485abb17dff408bd73ad.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/e205784d50a344d391c347f37d428eb7.png">