一个给定点的导数不过就是一条切线的斜率轻吻了那个点。
A derivative at a given point is just the slope of the tangent line that kisses that point.
我希望我是你的导数，这样我就能成为一条切线，躺在你的曲线上。
I wish I was your derivative so I could lie tangent to your curves.
历史上，速度问题和切线问题是形成导数概念的基础。
In the history, the speed question and the tangent question are form the derivative concept the foundation.
应用推荐