Can anyone help me to simplify this equation
I have troubles in simplfying this equation normally in Mathcad15 it can be simplfied as following equation shown in the picture. However this doesn´t work on mathcad prime as shown on next picture.


I have troubles in simplfying this equation normally in Mathcad15 it can be simplfied as following equation shown in the picture. However this doesn´t work on mathcad prime as shown on next picture.


As already written above - you need to define variable i
Thats also what the error message is telling you.
I am not sure what you are trying to achieve, but maybe you are looking for something like this:

You could also use

for the same result.
If this is, as I think, what you are looking for and if you need that kind of calculation more often you may consider writing a small utility function like this, which you can use on various vectors of arbitrary size and without having to define ranges, etc.:

Worksheet in P6 format attached
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