Name: ゼロファクター - 数字マニア (Zero Factorial - Numberphile)
Uploaded: 2021-01-14T04:55:14.000Z
Duration: 7 min 36 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

現在進行形

JAMES GRIME: Today, we're going to talk about one of the

questions that we get sent in a lot at Numberphile, and the

命令形

question is-- well, Brady, what's the question?

BRADY HARAN: The question is, why does 0 factorial equal 1?

So let's start off with a quick recap of what a

For our whole number, let's pick a number n--

n factorial, which is written like that. n with an

It's n multiplied by n minus 1 multiplied by n minus 2

and you keep going down, and you'll go down to 3

The question we've been asked is what is 0 factorial.

So the way you can answer this-- one of the ways you can

This pattern in particular, 4 factorial, is equal to 5

If you can see that, if I take 5 factorial here and divide by

5, that means I can knock off that 5, and you

So 5 factorial divided by 5, or 120 divided

3 factorial is going to be 4 factorial divided by 4.

2 factorial, 3 factorial divided by 3, 6, which we've

It's 1 divided by 1, and that is equal to 1.

BRADY HARAN: Who says the pattern has to be complete?

JAMES GRIME: I guess it doesn't necessarily have to be

BRADY HARAN: Let me continue the pattern first.

Does that mean negative 1 factorial would be next in

Another way to explain what 0 factorial might be.

Who says mathematicians don't make a lot of money?

Three objects here, and how many ways are there to arrange

That's one, that's two, or we could have this one here--

I think it was that one we didn't have at the front.

If we take one away, we have now two objects.

How many ways are there to arrange two objects?

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ゼロファクター - 数字マニア (Zero Factorial - Numberphile)

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