+0

# 0!=1???

0
278
2

Why does

0! = 1

?

Guest Apr 10, 2015

#2
+92254
+13

0!=1

I could just say that it is define that way which is certainly true.

or I could say that 0! is the number of ways that 0 items can be odered - that would be just one way.

Now

5C1 is the number of ways that 1 item can be  chosen from 5 it equals      $$^5C_1=\frac{5!}{1!(5-1)!}=\frac{5!}{1*4!}=5\\\\$$

5C0 is the number of ways that 0 item can be  chosen from 5 it equals  [the answer has to be 1 there is only one way of chosing nothing]

$$\\^5C_0=\frac{5!}{0!(5-0)!}=\frac{5!}{0!*5!}=\frac{1}{0!}\\\\  the only way this can work is if 0!=1\\\\ so\\\\ 0!=1$$

Melody  Apr 10, 2015
Sort:

#1
+85958
+5

Here's an  informal "proof"....

3! =  4! / 4

2! =  3! / 3

1!  = 2!/ 2

So, by extension

0!   = 1! / 1    = 1

CPhill  Apr 10, 2015
#2
+92254
+13

0!=1

I could just say that it is define that way which is certainly true.

or I could say that 0! is the number of ways that 0 items can be odered - that would be just one way.

Now

5C1 is the number of ways that 1 item can be  chosen from 5 it equals      $$^5C_1=\frac{5!}{1!(5-1)!}=\frac{5!}{1*4!}=5\\\\$$

5C0 is the number of ways that 0 item can be  chosen from 5 it equals  [the answer has to be 1 there is only one way of chosing nothing]

$$\\^5C_0=\frac{5!}{0!(5-0)!}=\frac{5!}{0!*5!}=\frac{1}{0!}\\\\  the only way this can work is if 0!=1\\\\ so\\\\ 0!=1$$

Melody  Apr 10, 2015

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