in a few words the main ideas?"

为我总结一下上节课的内容吗"
So I would like to do that.

我很乐意这么做
What I did last time

上节课的内容
was to show you how to handle motion in more than one dimension.

是用多维矢量描述运动
I picked for it two dimensions as the standard way to explain it.

我选取二维的情形作为标准模型来讨论
By the way, I would like to make one recommendation.

顺便提一句我有个建议
If you guys are coming in a little late,

如果你们上课来迟了
don't worry about submitting the homework.

就先别急着交作业
Just come in and settle down,

进来以后就赶紧坐下来
because it's very hard to lecture with this amount of traffic.

你们这样乱糟糟的我讲不下去
I do try to start a few minutes late,

我已经推迟上课好几分钟了
but I also have to finish a few minutes early

我还得提前下课