若随机变量， 且则二维随机变量服从二维正态分布。https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/06902c8739054c2686716051f5d8b3fd.png

x(t)的频谱为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/5bcfe4175fcb4fabbdb5f40d00b5343e.png"/>，则<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/45b1670ebd6245ff99cc376a8048a645.png" />的频谱为（ ） A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/09bc7326832a4a1fba983e74c6d85d35.png"/> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/95fca346a74e4a6cbba601cd6d9e26bf.png"/> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/6bf6b83111ad45efac7eb9a37a245c68.png"/> D: 其余选项都不对

设，且，则（ ）https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/54eb7bb314af4d48acd79bdaed0a3a54.png

历史曲线构件的图标是( )。 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/dfb6b619f35547c590f6e6c6aab95b3f.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/e7e0aaa5f6e84ba89410cc93b06a451a.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/354425393230484ab64d64a718bd9bad.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/1f794e99ed004e3190fa5181c32fe4e8.png" />

下面的表达式中，正确有？ A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/0e169fdf5e354dd4af80ea6386ddeca5.png"/> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/5124889b558b4186ba4140ca7692d717.png"/> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/f3d2d0d80b744f74899371cae0395a71.png"/> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201911/2af6ef9203e94ea2b993e1ad4d99e5d2.png"/>