a(n+1)=4(n+1).an/(3an+n)3an.a(n+1) + na(n+1) = 4(n+1)an3 + n/an= 4(n+1)/a(n+1)4(n+1) [ 1/a(n+1) -1/(n+1) ]= n[ 1/an -(1/n)][ 1/a(n+1) -(1/(n+1) ]/[ 1/an -(1/n)] = (1/4)[n/(n+1)][ 1/an -(1/n)]/[ 1/a(n-...我早就做出来了，不过还是很感谢