总而言之，我们所做的就是求二阶导数。

And all we did, further, is take that second derivative.

youdao

那么二阶导数判定是怎样的呢？

So, what does the second derivative test say?

youdao

它就是位置，对时间的一阶导数。

That's the first derivative of the position versus time.

youdao

它的二阶导数就是这个恒加速度。

The second time derivative is the constant acceleration.

youdao

他们说二阶导数转为正值了。

The second derivative, they say, is turning positive.

youdao

我们不可以用2阶导数来观察或者别的什么方法。

We cannot use second derivative tests or anything like that.

youdao

在此方程中，弥散项和对时间的导数为分数阶导数所代替。

In this equation, the diffusion is a fractional order derivative of time and space.

youdao

我是说现在已经有两个一阶偏导数。

I mean we already have two first derivatives.

youdao

我是说现在已经有两个一阶偏导数。

I mean we already have two first derivatives.

youdao