信号 如图所示，求其频谱。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/e7cf021b113341e4bb5ee98d7d12e0f2.png

已知其收敛域为：求其原序列。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/9d891687ee7344a88811f610aba238bc.png

设<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/caa2009d65b9414e9eee2f311038ed51.png"/> 为系统输入，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/af57e24c7bb247e29a81996211b39e9d.png"/>为系统输出，则下列关系式中为线性时不变系统的是（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/6d8d3ed4bbb5472d8ad95cf86ff40033.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/553b7fd10b744a38859127a91414813b.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/e59a6933e2c647d4b5c12b2ebb0a0ff6.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/4835c010dc244facb01784095e9bd080.png"/>

有一LTI离散系统，其差分方程为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/56de766141c64b2f93809c0d9a707900.png" />其传输算子为？ A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/47db6248d80c41579452e5265852f031.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/d3ee5176fb5d4c55af1b973b3bb6c66b.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/10f3f84e8c0648d292fdfd7a07edac2e.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/6c0a80355cf4445b89706482a3cd4891.png" />

已知离散信号 的 z 变换为 ，其收敛域为 ，求其原序列。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/ec368276ef7740628c0d86426523d30a.png