f⑴,f⑵,f⑶,f⑷的值都是2cos(2π/3+2α).
一般地,f(n)=2cos(2π/3+2α).
证明:f(n)=cos[(3n+1)/3*π+α)]+cos[(3n-1)/3*π-α]
=2cos(2nπ)cos(2π/3+2α).