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

如果这是 7 除 7 减 2 阶乘，我们将有 7 乘以 6。

Instead of factorial time, it takes linear time.

它不是阶乘时间， 而是线性时间。

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

所以 k 阶乘可以写成 k 乘以 k 减 1 阶乘。

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

所以这可以改写为 k 乘 k 减 1 阶乘。

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 的阶乘是多少？

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 阶乘。

That's all this factorial stuff here.

这就是所有这些阶乘的东西。

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

乘以 n 减 k 阶乘 p 到 k 乘以 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 的阶乘，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 个阶乘，我会告诉你这是如何发生的。