设<img src="https://static.zxtiku.com/wangke/imgs/topic/1d80de7479ba09a9ae4054b0e0ec4a92.jpg"/>是2维欧氏空间<img src="https://static.zxtiku.com/wangke/imgs/topic/0fb3b0edbcfa50eadfa375d374e170bc.jpg"/>的一组标准正交基，<img src="https://static.zxtiku.com/wangke/imgs/topic/559b3991545277d56c9a41ec038fd539.jpg"/>，且<img src="https://static.zxtiku.com/wangke/imgs/topic/360eaaf662afe46dfca71e8696271eab.jpg"/>，<img src="https://static.zxtiku.com/wangke/imgs/topic/2679a1a59a099b65c68eaba1694dec4d.jpg"/>，则<img src="https://static.zxtiku.com/wangke/imgs/topic/e62d331aeaa97beb3a3548f70b64655d.jpg"/>（）。