Finding the sum of a series without symsum

I'm trying to do the system sum of this equation, but all I've found is the command symsum to do this. However, I don't have the toolbar that this command comes with. Is there any way to either use this command or any other commands I can use to do this?

This is what I got so far. Any help is appreciated.

com_cos = symsum((((-1) ^ k) * x_val ^ (2 * k)) / factorial(2 * k), k = 1..Infinity);

Answer 1

[Roger Stafford]

You don't need 'symsum' to evaluate that series. It's easy to see that its sum is

com_cos = cos(x_val)-1

just by inspection.

[Matthew Olivo]

Thank you!

Answer 2

[Walter Roberson]

http://blogs.ubc.ca/infiniteseriesmodule/units/unit-3-power-series/taylor-series/the-maclaurin-expansion-of-cosx/

[Matthew Olivo]

Thank you!