Write the permutation and combination formulas using latex

[temaire]

How do you write the permutation and combination formulas using latex. This is the best I can do:

$$n_P_r=\frac{n!}{(n-r)!}$$

 

[cristo]

You mean like this: $$n \choose r$$ or $$^n\mathrm{C}_r$$ ?

 

[temaire]

Yes, that's what I meant, but I am used to writing down like this:

http://img88.imageshack.us/img88/7682/formula2nj1.png

 

[cristo]

Ok, how about this then: $$_n\mathrm{C}_r \hskip5mm _n\mathrm{P}_r$$

 

[temaire]

Thanks, that's what I needed.

 

[temaire]

Out of curiosity, are you good at perms. and combs.? Because I have a question on the the Precalc. forum that hasn't been answered yet. If not, it's ok, because I can wait.