A、∑X=0
B、<img src="https://img.ppkao.com/2016-07/tangyingmei/2016072517073437990.jpg">
C、<img src="https://img.ppkao.com/2016-07/tangyingmei/2016072517073795469.jpg">
D、∑Y=0
E、<img src="https://img.ppkao.com/2016-07/tangyingmei/2016072517074098359.jpg">
查看答案