已知数列｛an｝前n项和Sn=n^2+2n (1)求数列的通项公式an (2)设Tn=1/a1a2
已知数列｛an｝前n项和Sn=n^2+2n
(1)求数列的通项公式an
(2)设Tn=1/a1a2+1/a2a3+…+1/(anan+1)求Tn