Change the independent variable, find the change in the function, take the ratio and that's the derivative.

改变自变量,算出函数的变量,计算比值,这就是求导

耶鲁公开课 - 基础物理课程节选

I put it there because, well, I think the major chain bookstores fulfill an important function but I also like to support independent bookstores.

我推荐这个书店是因为,我认为,虽然主流的连锁书店,起到了很重要的作用,但是我仍然想支持一下独立书店

耶鲁公开课 - 金融市场课程节选