If this was 7 over 7 minus 2 factorial we would have 7 times 6.

如果这是 7 除 7 减 2 阶，我们将有 7 以 6。

Instead of factorial time, it takes linear time.

它不是阶时间， 而是线性时间。

So k factorial could be written as k times k minus 1 factorial.

所以 k 阶可以写成 k 以 k 减 1 阶。

So this could be rewritten as k times k minus 1 factorial.

所以这可以改写为 k k 减 1 阶。

And here we can make a little bit of a simplification because what's k divided by k factorial?

在这里我们可以稍微简化一下，因为 k 除以 k 的阶是多少？

So we could rewrite n factorial using the same trick up here.

所以我们可以在这里使用相同的技巧重写 n 阶。

That's all this factorial stuff here.

这就是所有这些阶的东西。

Times n minus k factorial times p to the k times 1 minus p to the n minus k.

以 n 减 k 阶 p 到 k 以 1 减 p 到 n 减 k。

So we'll take the factorial of 6 and we'll divide it by-- put a parentheses here.

所以我们将取 6 的阶，然后将它除以 -- 在这里放一个括号。

If this had 3 we would do 3 factorial, and I'll show you how that can happen.

如果它有 3，我们会做 3 个阶，我会告诉你这是如何发生的。

5 factorial is 5 times 4 times 3 times 2 times 1.

5阶是5以4以3以2以1。

And actually, it turns out that it's 2 factorial.

实际上，它是 2 的阶。

And as you'll see it's actually 2 factorial ways that it can happen.

正如您将看到的，它实际上可以通过两种阶方式发生。

Divided by 2 factorial times e to the minus 9 power.

除以 2 阶 e 的负 9 次方。

So times lambda to the k k over k factorial.

所以以 lambda 到 k k 阶。

So the n minus k will become b minus a factorial.

所以 n 减去 k 将变成 b 减去一个阶。

This would have an N factorial complexity - that is the number of nodes, times one less, times one less than that, and so on until 1.

这将具有 N 阶复杂​​度 - 即节点数，减一，再减一，依此类推直到 1。

So it's a factorial of how many we're choosing from, how many shots we're taking, and the Excel function for that is fact.

所以它是我们从中选择的数量、我们拍摄的照片数量的阶， 而 Excel 函数就是事实。

So that's why I got the 3 factorial.

所以这就是我得到 3 阶的原因。

So you end up with 1 times lambda k over k factorial.

所以你最终得到 lambda k 的 1 倍于 k 的阶。