Re: Summations

*To*: mathgroup at smc.vnet.net*Subject*: [mg78248] Re: Summations*From*: dh <dh at metrohm.ch>*Date*: Wed, 27 Jun 2007 05:17:56 -0400 (EDT)*References*: <f5qme1$46g$1@smc.vnet.net>

Hi Sima, what problem do you have that you can not do it yourself? Sum[i a^i,{i,1,n}] gives (a (1-a^n-a^n n+a^(1+n) n))/(-1+a)^2 Sum[i n^i+n^3,{i,1,m}] gives m n^3+(n (1-n^m-m n^m+m n^(1+m)))/(-1+n)^2 hope this helps, Daniel Sima wrote: > Can someone please solve this summations: > > Summation(from i=1 to n) (i * a ^ i) > > Summation(from i=1 to m) (i * n ^ i + n ^ 3) > > you can mail me sollutions. Thanks > >