11.(-1ⓧ2)ⓧ3=[2²-(-1)×2]ⓧ3=6ⓧ3=3²-6×3=9-18=-912.a2=1/(1-a1)=1/[1-(-½)]=⅔a3=1/(1-a2)=1/(1-⅔)=3a4=1/(1-3)=-½数列是以3为周期的周期数列。a2016=a(3×672)=a3=3
