Re: Solve equation with summation?

*To*: mathgroup at smc.vnet.net*Subject*: [mg123041] Re: Solve equation with summation?*From*: Dana DeLouis <dana.del at gmail.com>*Date*: Mon, 21 Nov 2011 04:28:43 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Hi. A simpler example than Solve for this issue might be to just multiply. t = Sum[Subscript[a, i]/x, {i, 1, n}] If you multiply the above by x, then the x should cancel. However, it still remains unevaluated. FullSimplify[x*t] x*Sum[Subscript[a, i]/x, {i, 1, n}] As a side note, saying that x was not zero didn't help either. x * Sum[Subscript[a, i]/x, {i, 1, n}, Assumptions -> x != 0] <unevaluated> Because if x was zero, then you have Power::Infy Sum[Subscript[a, i]/0, {i, 1, n}] Power::infy:Infinite expression 1/0 encountered. >> ComplexInfinity = = = = = = = On Nov 18, 6:22 am, Ivan <ive... at gmail.com> wrote: > For a summation like \sum_{i=1}^n a_i/x = 1, > > Solve[Sum[Subscript[a, i], {i, 1, n}]/x == 1, x] > > gives a correct solution. > > However, by putting x into the summation: > > Solve[Sum[Subscript[a, i]/x, {i, 1, n}] == 1, x] > > gives an empty set, why?

**Follow-Ups**:**Re: Solve equation with summation?***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>