我想請問老師第31題如何做 謝謝您 Sn= Sigma{k=1 k=n} 1/(1+2+3...k ) =Sigma{k=1 k=n} 1/(k(k+1)/2) =2 Sigma{k=1 k=n} 1/(k(k+1)) =2(1/(1*2) +1/(2*3) +1/(3*4) +............+1/(n*(n+1)) ) =2(1/1 -1/2 + 1/2 -1/3 +...................+1/n -1/(n+1) ) =2(1/1- 1/(n+1))= 2n/(n+1) lim{n->infinity} Sn= lim{n->infinity} 2n/(n+1)...