What does (x choose 2) mean
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What does (x choose 2) mean

[From: ] [author: ] [Date: 11-04-22] [Hit: ]
r) = n! / ( r! (n-r)!So,C(x,2) = x!......
So I'm trying to understand this notation and it's meanings:
(x)
(2)

But pretend the two parenthesis on each side are put together so it's "x choose 2".

I really have no idea how to use this!

-
It's the combinations of X things two at a time.

In general, Combinations is nCr, or C(n,r), which is the combinations of n things, r at a time.

The general formula is:

C(n,r) = n! / ( r! (n-r)! )

So, x things two at a time would be:

C(x,2) = x! / ( 2! (x-2)! )

Naturally, you need to know the numeric value of x before you can calculate the exact number of combinations.
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