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What is a "!" in math and how is it used?

 Dec 19, 2014

Best Answer 

 #2
avatar+128089 
+5

Notice that we can prove - in an offhand manner - that 0! = 1

Note

3! = 4! / 4   and

2! = 3! / 3   and

1! = 2! / 2   

So

0!  = 1! / 1   = 1/ 1   = 1

 

 Dec 20, 2014
 #1
avatar+23245 
+5

"!" means "factorial" and it's a fast way to indicate multiplication:

0!  =  1                     (a special case)

1!  =  1                     (a special case)      also:  1!  =  1 x 1!

2!  =  2 x 1  =  2                                   also:  2!  =  2 x 1!

3!  =  3 x 2 x 1  =  6                              also:  3!  =  3 x 2!

4!  =  4 x 3 x 2 x 1  =  24                       also:  4!  =  4 x 3!

5!  =  5 x 4 x 3 x 2 x 1  =  120                also:  5!  =  5 x 4!

etc. 

Another way to define !:  0! = 1  and, if n is a whole number > 0:  n! = n x (n - 1)!

 Dec 19, 2014
 #2
avatar+128089 
+5
Best Answer

Notice that we can prove - in an offhand manner - that 0! = 1

Note

3! = 4! / 4   and

2! = 3! / 3   and

1! = 2! / 2   

So

0!  = 1! / 1   = 1/ 1   = 1

 

CPhill Dec 20, 2014

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