设随机变量X~N(4,2)，则其特征函数为().
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举一反三
- 为使锅垢中难溶于酸的CaSO4转化为易溶于酸的CaCO3，常用Na2CO3处理，反应式为CaSO4+CO32-<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/88320eab77594b6abf0039ab0efe3c57.png" />CaCO3+SO42-，此反应的标准平衡常数为（）。 A: K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4)·K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3) B: K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3)/K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4) C: [K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4)·K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3)]1/2 D: K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4)/K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3)
- 10人中至少有2人同生日的概率是多少？（1年按365天计算）() A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/f3b577db2dd0429b9eab51dff5644b23.png" > B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/6f30552128e14bfb89b26b30ac2b72db.png" > C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/fa8f9ba9bd2d4a40b7d007fd9e9988fd.png" > D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/05a12b5d4da04e2c9ea779b313981c83.png" >
- 从数字<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/2d61a913ea754ceab9283348404e99b8.png" >中任取两个不同的数字，则这两个数字之差的绝对值的数学期望为()。 A: 1 B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/7da33d3a3bd54a188acf94dfdbab4f56.png" > C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8d44a97a0d141198c56ce68511897c9.png" > D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/fa3d4d77c7ea4487a9fd484134badc5e.png" >
- 下列逻辑命题正确的是（）。 A: 若Y=A+B则<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/2ac821feb3d7451a8c7c69c97de1ca39.png">=<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/d900fde7b3dc4b2ea24859c0712ddd0c.png"> B: 若A+B=A+C则B=C C: 若Y=A+B则<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e305d54dd8c94adfaf570a2f0e6d4421.png">=<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/3cb33b429abf4ec397173f58dcdd37af.png">+<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/87aa5698238b4b66b9264426769b7b17.png"> D: 若AB=AC则B=C
- 某最小相位系统的开环对数幅频特性曲线<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/bcd21e42b27341478945568b99d0e0e1.png" >如图所示，则其开环传递函数和相角裕度分别为（）。<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/84e4b98286924479ae7d38d3b0e5fd2f.png" > A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/b0eda84a8f794aaab38a2ca259435434.png" > B: 0° C: 16.3° D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/aa67284249764b51bb1c9fb836c2a9aa.png" >