He got a B minus on the project, because his teacher reportedly thought it was unoriginal.

他的这面国旗拿到了个B-的分数, 因为据报道, 他的老师认为这有模仿之嫌。

Minus b minus 1, these would cancel out.

减 b 减 1，这些会抵消。

So the 1's cancel out and you get b minus a.

所以 1 抵消了，你得到 b 减去 a。

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

所以 n 减去 k 将变成 b 减去一个阶乘。

You can imagine if this was a minus b, it would be a squared minus 2ab plus b squared.

您可以想象，如果这是 a 减 b，它将是 a 的平方减去 2ab 加上 b 的平方。

I have b things and I want to choose a things from them, how many different ways can I-- times p to the a times 1 minus p to the b minus a.

我有 b 个东西，我想从中选择一个东西，我可以有多少种不同的方法--乘以 p 到 a 乘以 1 减去 p 到 b 减去 a。