an = cos (npi/2). If convergent find limit of sequence?

The sequence is: cos (π/2), cos (π), cos (3π/2), cos (2π), ...

or: 0,-1,0,1,0,-1,0,1, ... Since cos (nπ/2) oscillates between - 1 and 1 as n tends to infinity, this sequence is divergent (limit does not exist).