已知信号<img src="https://static.zxtiku.com/wangke/imgs/topic/520f3b391269ba3683f13140e80d735a.png"/>的波形如图所示，下列表达式中错误的是( )<img src="https://static.zxtiku.com/wangke/imgs/topic/f9d31d86037bf0074a727c2290a2492b.png"/>