easy stuff (1 Viewer)

[shuning]

prove

 

[lyounamu]

prove

n!/((n-r)!r!) + n!/((n-r-1)!(r+1)!)
= (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)

 

[Drongoski]

 

[shuning]

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