设e1,e2是两个单位向量,若e1与e2的夹角为60°,求向量a=2e1+e2与 发布时间:2017-04-14 16:00 │ 来源:www.tikuol.com 题型:解答题 问题: 设e1,e2是两个单位向量,若e1与e2的夹角为60°,求向量a=2e1+e2与b=-3e1+2e2的夹角.
题型:解答题 The great lady devoted most of her time _____ the poor. [ ]A. to help B. to helpingC. for helping D. in help 查看答案