Need help with formula in Excel XP

[Danchops]

I'm trying to create a formula in a cell that, given x, y, and n in other cells, calculates x*y + (x*y)*y + ((x*y)*y)*y + (((x*y)*y)*y)*y ... n times. Anyone know how to do that?

Any help is greatly appreciated.

[ramana]

Hi,

Your problem seems to be sum of geomeric expression.

Looking into your question we can take x as a common factor and the
equation can be written as X*(y+y^2+y^3+......+y^n).

Say in cell A1=X
Cell B1=y
Cell C1=n
now youcan write the formula as =A1*((B1^(C1+1)-1)/(B1-1)+1)

Hope that this might solve your problem.

Thanks and Regards

Ramana

Danchops wrote:
> I'm trying to create a formula in a cell that, given x, y, and n in
> other cells, calculates x*y + (x*y)*y + ((x*y)*y)*y + (((x*y)*y)*y)*y
> ... n times. Anyone know how to do that?
>
> Any help is greatly appreciated.
>
>
> --
> Danchops
> ------------------------------------------------------------------------
> Danchops's Profile: http://www.excelforum.com/member.php...o&userid=27942
> View this thread: http://www.excelforum.com/showthread...hreadid=474426

[ramana]

Err... just a small correction i kept +1 instead of -1.
Now notedown the formula.

=A1*((B1^(C1+1)-1)/(B1-1)-1)

where ^ denotes to the power of and to get this Press Shift+6 and then
press space.

rgds

Ramana

[Ron Rosenfeld]

On Fri, 7 Oct 2005 22:46:51 -0500, Danchops
<Danchops.1wkf2b_1128744309.7729@excelforum-nospam.com> wrote:

>
>I'm trying to create a formula in a cell that, given x, y, and n in
>other cells, calculates x*y + (x*y)*y + ((x*y)*y)*y + (((x*y)*y)*y)*y
>.. n times. Anyone know how to do that?
>
>Any help is greatly appreciated.


Try this:

=x*SUMPRODUCT(y^ROW(INDIRECT("1:" & n)))

Substitute numbers or cell references for x, y and n


--ron