How to express cos((n*pi*)/2))

[ETT]

I am doing PDE, heat equation with Homogenous BC's...

I am solving my constant, Bn, but I do not know how to express cos((n*pi*)/2)).
I know that cos(n*pi) is (-1)^n...but what is cos((n*pi*)/2)).


Thank you.

 

[Mark44]

Well, it's one of -1, 0, or 1, depending on the value of n.

Make a table with values of n and the corresponding values of cos(n*pi/2), and see if you can discover a pattern.