Uh oh! Wolfram|Alpha doesn't run without JavaScript.
Please enable JavaScript. If you don't know how, you can find instructions
here
.
Once you've done that, refresh this page to start using Wolfram|Alpha.
(sum i (sum cos((2 (n - i) j pi) / k), j = 0 to k - 1), i = 1 to k - 1) where k = 3
Natural Language
Math Input
Extended Keyboard
Examples
Upload
Random
