某医院用一种中药治疗高血压，记录了50例治疗前后病人舒张压数据之差，得其均值为16.28，样本标准差为10.58，
。假定舒张压之差服从正态分布，问在
水平上该中药对治疗高血压是否有效，其假设为
。（ ）
。假定舒张压之差服从正态分布，问在水平上该中药对治疗高血压是否有效，其假设为。（ ）
举一反三
- 系统的开环传函为<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/4c0fd44e4fd34ba5abebcf5cf4075e5b.png" />，根轨迹和虚轴的交点及相应的根轨迹增益为（ ）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/1a01ea0a12204b8395a0b5b77f6dff14.png" />，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/5973aa4feb8b449e936c4db36ba0f235.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/3212607aceba42119e02c092ee59c4c9.png" />，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/5e06d749351c40758f2d90bd5503ac41.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/646b41ca995f4f9883b1d2c4a17a1b4c.png" />，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/f268e2b90534408293cc995f99bf8907.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/212d583db0b74c5a84acfc955c422863.png" />，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/5e06d749351c40758f2d90bd5503ac41.png" />
- 考虑AR(2)模型<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/9c19d336a086430cab947cf3a40c8047.png" />,则AR特征方程的根为（ ）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/b8d42e894377426eaca4f3a382c0569c.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/cb2410db797c4dc5870eb9ab1dfae59e.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/505155f9e5654d3294291a0f104fd54f.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/ff900163e913414384b61dbd55a0c36e.png" />
- 函数<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/82f8c419da9c41f9b86e94ae2b2bcaf5.png" />的拉普拉斯逆变换为（ ）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/ed47adacefc64ac5afdfd39b57836c33.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/63ca53741edf465089db1557fb3d842a.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/744c576c1fe24e83aca105adcd700936.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/9699edb62c4c452eaac4b533c11e951a.png" />
- <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/78ba624fbf734c1d9af5e00e4b9c2044.png" />的Laplace变换为（ ） A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/ce12c2b6f25745f3a613f524ab3f0a15.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/1ac3b7dcc46848719b73c1751203b3f3.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/c5e3953d9bb040dd9b99aa8b1a9909bb.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/0ba32254e04f49eeaf592ef9fcbe6142.png" />
- <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/2f2539faa2cb42939c3a676ef42f909a.png" />的Laplace变换为（ ） A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/d7d45e2a8a32472090116ea10729421f.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/ecf689c55bf744a1be41c63e466ef916.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/a112c4e5f6c9443395f3fe1df0cb38b9.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202105/38f822b0273a407ba6d2d6b7351f4bdf.png" />