我们来用方向导数，来描述一下相同的东西。

Let's say the same thing in terms of directional derivatives.

youdao

想象一下，一个导数作为车上的车速计。

Imagine a derivative as the speedometer on a car.

youdao

想象一下，一个导数作为车上的车速计。

Imagine a derivative as the speedometer on a car.

youdao