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Math Help - prove

  1. #1
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    prove

    prove that

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

    does that make sense?

    not sure how to write the question properly
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  2. #2
    Member eXist's Avatar
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    Not sure about your notation, check out the latex tutorial to help write equations more appropriately.

    http://www.mathhelpforum.com/math-he...-tutorial.html
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  3. #3
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    ok thanks for tip this is my next attempt at the question

    [tex]\left(\begin{array}{cc}n&r\end{array}\right)\\cdot \\^r\mbox{P}\_r\=\^n\mbox{P}\_r[\math]
    Last edited by deej813; September 2nd 2009 at 01:17 AM.
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  4. #4
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    ok can anyone understand that and tell me what i did wrong in writing it
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  5. #5
    Member eXist's Avatar
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    [\math] should be [/tex] with a forward slash
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  6. #6
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    \left(\begin{array}{cc}n&r\end{array}\right)\\cdot  \\^r\mbox{P}\_r\=\^n\mbox{P}\_r

    like that?
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  7. #7
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    now what did i do wrong??
    do you understand the question enough to help without me trying to write it again
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  8. #8
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    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?

    Grandad
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  9. #9
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    yes
    thats it
    thankyou
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