However, we'll see one later using a cool trick, and multi-variable calculus. So, for now, we'll just leave the formula like that, and we don't know how long it is.

但之后我们会用很酷的方法解决它，以及多元微积分，但目前，我们只需要写到这就行了，我们还不懂如何计算它。

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You may want to note that this is the first volume, and that the second volume is also worth getting: Calculus, vol. 2: Multi-Variable Calculus and Linear Algebra with Applications.

你会发现这是他它的第一卷，并且第二卷也值得去读：微积分卷2：多远微分与与线性代数及其应用。

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