已知信号<img src="https://static.zxtiku.com/wangke/imgs/topic/5efbdbb864ad10b4d831958fdf0946d9.png"/>,信号<img src="https://static.zxtiku.com/wangke/imgs/topic/d9484f91121a04575c62d6e5cced9ee1.png"/>=( )