已知数列{an}的前n项和为Sn,a1=-2/3,满足Sn+1/Sn+=an

s1=-2/3 s2+1/s2+2=a2=s2-a1 s2^2+1+2s2=s2^2+2s2/3 s2=-3/4 s3+1/s3+2=a3=s3-s2 s3^2+1+2s3=s3^2+3s3/4 s3=-4/5 s4+1/s4+2=a4=s4-s3 s4^2+1+2s4=s4^2+4s4/5 s4=-5/6 Sn=-(n+1)/(n+2)