Math Help - prove

1. prove

prove that

( n ) . r = n
( r ) Pr Pr

does that make sense?

not sure how to write the question properly

2. Not sure about your notation, check out the latex tutorial to help write equations more appropriately.

http://www.mathhelpforum.com/math-he...-tutorial.html

3. ok thanks for tip this is my next attempt at the question

$$\left(\begin{array}{cc}n&r\end{array}\right)\\cdot \\^r\mbox{P}\_r\=\^n\mbox{P}\_r[\math] 4. ok can anyone understand that and tell me what i did wrong in writing it 5. [\math] should be$$ with a forward slash

6. $\left(\begin{array}{cc}n&r\end{array}\right)\\cdot \\^r\mbox{P}\_r\=\^n\mbox{P}\_r$

like that?

7. now what did i do wrong??
do you understand the question enough to help without me trying to write it again

8. Hello deej813

I think you might mean:

$\binom{n}{r}\times\,^r\mbox{P}_r =\, ^n\mbox{P}_r$

In which case, note that $^n\mbox{P}_r=\frac{n!}{(n-r)!}$

and in particular, if $n = r,\, ^r\mbox{P}_r=\frac{r!}{0!}=r!$, since $0! = 1$.

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

So $\binom{n}{r}\times\,^r\mbox{P}_r = \frac{n!}{r!(n-r)!}\times r! =\,^n\mbox{P}_r$

Is that it?