Syntax for a series summation

[upshaw211]

I need to find out how to input a series summation in Excel, similar t
Sigma notation.

The formula I need to input is [(x*C)^i]/factorial(i) From (i=0) t
(i=x-1) and where C is a constant.

The length of the series depends on the value of x, but x is a variabl
which can be assigned different values, so I cannot simply write out th
whole formula based on a certain value of x.

Any help will be GREATLY appreciated. Thanks

 

[Myrna Larson]

To simulate the summation, you need an array formula. Here are two
possibilities.

I've assumed your constant is in $C$1 and X is in $X$1:


=SUM((($X$1*$C$1)^(ROW(INDIRECT("$1:$"&$X$1))-1))/FACT((ROW(INDIRECT("$1:$"&$X$1))-1)))


=SUM((($X$1*$C$1)^(ROW(OFFSET($A$1,0,0,X1,1))-1))/FACT((ROW(OFFSET($A$1,0,0,X1,1))-1)))

Type in one or the other of those formulas, then press CTRL+SHIFT+ENTER (not
just ENTER) to enter it. In the formula bar, you'll see braces ( {} ) around
it if you've entered it correctly. With the constant = 3 and X = 10, I got
76106409.57

This is the same result I got when putting the numbers 0-9 in A1:A1, and the
formula =(($C$1*$X$1)^A1)/FACT(A1) in B1 and copying through B10, then summing
B1:B10.