Tính tổng S=1/2018.(C 2018 1)^2+2/2017.(C 2018 2)^230/30Tính tổng S=12018C201812+22017C201822+...+20172C201820172+20181C201820182S=12018C40362018S=12018C40362019S=20182019C20181009 S=20182019C40361008Giải thích