- #1
pp123123
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I came across some summation but have no idea how to simplify it.
$\sum_{x=0}^{\infty} \binom{x+r-2}{r-2}(1-p)^{x}=p^{1-r}$
Why is it so?
$\sum_{x=0}^{\infty} \binom{x+r-2}{r-2}(1-p)^{x}=p^{1-r}$
Why is it so?