(n+1)a(n+1)=2(n+2)an+3n²+9n+6(n+1)a(n+1)=2(n+2)an+3(n+1)(n+2)等式两边同除以(n+1)(n+2)a(n+1)/(n+2)=2an/(n+1) +3a(n+1)/(n+2) +3=2an/(n+1)+6=2[an/(n+1)+3][a(n+1)/(n+2) +3]/[an/(n+1)+3]=2,为定值a1/(1...接上面的第二问bn=3(n+1)/an,{bn}的前n项和Tn<5/3