[texhax] \binom
Rolf Turner
r.turner at auckland.ac.nz
Sun Mar 1 23:21:27 CET 2009
On 2/03/2009, at 10:47 AM, P. R. Stanley wrote:
> An excellent answer! That's exactly the sort of info I'm after!
> Cheers,
> Paul
>
>> Hi
>>> What does it do? What do you get when you compile $\binom{3}{4}$
>>> in a
>>> document? Thanks
>>> Paul
>>
>> It sets a 3 above a 4 and encloses them both in a single pair of
>> sufficiently
>> tall parentheses. The 3 and the 4 are the same size as each other.
>> You
>> probably already know what it denotes, but just in case you don't,
>> here's one
>> way to describe it: $\binom{n}{r}$ denotes the coefficient of $x^r
>> y^{n-r}$ in
>> the expansion of $(x + y)^n$.
There's a wee problem in that \binom{3}{4} would denote the
coefficient of
x^4 y^{-1} in the expansion of (x + y)^3 --- and there isn't one.
As far as I can discern there is no way to make \binom{3}{4}
meaningful, since
Gamma(0) is undefined.
Now \binom{4}{3} --- that's a different story! :-)
cheers,
Rolf Turner
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