已知数列{an}中,Sn是前n项和,满足Sn+an=n,(n=1,2,3...)求a1,a2,a3的值.求数列{an}的通向公式

n=1,S1+a1=1,2a1=1,a1=1/2n=2,S2+a2=2,a1+2a2=2,a2=3/4n=3,S3+a3=3,a1+a2+2a3=3,a3=7/8∵Sn+an=n,(1)∴S（n+1)+a(n+1)=(n+1) (2)(2)-(1):2a(n+1)-an=1,a(n+1)=1/2an+1/2∴[a(n+1)-1]/[an-1]=【1/2an+1/2-1】/(an-1)=...