shuning
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easy stuff (1 Viewer)
- Thread starter shuning
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lyounamu
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n!/((n-r)!r!) + n!/((n-r-1)!(r+1)!)prove
= (n!(r+1))/((n-r)(n-r-1)!r!(r+1)) + (n!(n-r))/(r!(r+1)(n-r-1)!(n-r))
= (n!(n+1))/(r!(r+1)(n-r-1)!(n-r))
= (n+1)!/(r+1)!(n-r)! = (n+1)C(r+1)
shuning
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回复: Re: easy stuff
thx man.... got 2 the last 3rd step and made an error by copying down r instead of n LOL
thx man.... got 2 the last 3rd step and made an error by copying down r instead of n LOL