由s6/s4=1/4,得:6(a1+a6)/(4(a1+a4))=1/4;所以:(a1+a6)/(a1+a4)=1/6;(2a1+5d)/(2a1+3d)=1/6;a1/d=-27/10;s9/s3=3(a1+a9)/(a1+a3)=3a5/a2=3(a1+4d)/(a1+d)=3*13/(-17)=-39/17;
2)因为:sn-2sn-1=2而sn*sn+2/(sn+1)^2=sn*sn+1*sn+2sn+1/(sn+1)^4=2*2/(sn+1)^4;在sn-2sn-1=2中,令n=2得:a0*(a0+2)=2,所以a0=-1+sqrt(3),或a0 =-1-sqrt(3);