∵ ak+1=Sk+1+1/Sk+1+2所以Sk+1-Sk=Sk+1+1/Sk+1+2两边同时乘以Sk+1后得-Sk+1 Sk=1+2Sk+1(k+1)/(k+2) Sk+1=1+2sk+12sk+1-(k+1)/(k+2) sk+1=1所以Sk+1=-k+2/k+3
沟他龄
疫瓜拌
重谋匪