sigma notation (without lists or tables)

[tonyjnel]

Theta is the angle which is an input that changes depending on the problem. N is the number of magnets and is an input that changes depending on the problem.

I want to add up sin(theta)+sin(2*theta)+...sin((n-1)*theta)+sin(n*theta).

Now, I know how to do this by making a list that goes from 1 to n but I want this program to look professional (and I don't want you to have to change the length of the list or the formula if you have a different n value).

Is there a way to do this without making any tables or lists?

Thank you,

-Tony

[Cheeky Charlie]

How about:

=SUM(SIN(A2*ROW(INDIRECT("1:"&A1))))
Entered with Ctrl+shift+Enter, which should give curly brackets:
{=SUM(SIN(A2*ROW(INDIRECT("1:"&A1))))}

Where A1 = n and A2 = theta

Oh wait, this is much better:
=SUM(SIN(A2*ROW(OFFSET(1:1,0,0,A1))))
(also C+S+E)

Oh wait, this is the best:
=SUM(SIN(A2*ROW(INDEX(1:1,0):INDEX(1:65536,A1,0))))
(also C+S+E, and finally non-volatile - thank you decision models)

[mravi1]

I'm trying to do a similar thing but am having some trouble.

I want to add up: 3*(0.5)^1 + 3*(0.5)^2 + 3*(0.5)^3 + ... + 3*(0.5)^n

Can you help me with this?

[MrShorty]

mravi1: This forum tends to be very strict about starting your own thread rather than posting your question in an old thread. Please start your own thread.

I might also suggest you put "sum of a^x" or something like that into your favorite internet search engine. The answer to your question involves a relatively simple formula.

[shg]

I want to add up: 3*(0.5)^1 + 3*(0.5)^2 + 3*(0.5)^3 + ... + 3*(0.5)^n

There's a simple closed-form expression for this that doesn't require adding successive terms. Start your own thread and I'll be happy to post.

[FDibbins]

mravi1 welcome to the forum

As pointed out, unfortunately your post does not comply with Rule 2 of our Forum RULES. Do not post a question in the thread of another member -- start your own thread.

If you feel an existing thread is particularly relevant to your need, provide a link to the other thread in your new thread.

Old threads are often only monitored by the original participants. New threads not only open you up to all possible participants again, they typically get faster response, too.