       Re: Cancel[] and finite symbolic sums ?

• To: mathgroup at smc.vnet.net
• Subject: [mg102791] Re: [mg102763] Cancel[] and finite symbolic sums ?
• From: "David Park" <djmpark at comcast.net>
• Date: Thu, 27 Aug 2009 06:35:26 -0400 (EDT)
• References: <15915821.1251288036966.JavaMail.root@n11>

```You could try something like this:

Sum[W*Subscript[b, k], {k, 1, N}]/W
MapAt[Part[%, 1] # &, Part[%, 2], 1]

David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/

From: Andre Holzner [mailto:andre.holzner at gmail.com]

Dear experts,

I wonder what I'm doing wrong here...

I try to simplify the following expression: [Sum[W * Subscript[b, k],
{k, 1, N}]/W
by doing

Cancel[Sum[W * Subscript[b, k], {k, 1, N}]/W]

it looks like Mathematica just returns me the original expression: Sum
[W*Subscript[b, k], {k, 1, N}]/W

When I try a sum over b instead of Subscript[b, k], it seems to work
as expected:

Cancel[Sum[W * b, {k, 1, N}]/W]

gives:

b*N

Any ideas what I'm doing wrong ?

thanks,

Andre

```

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