熱心網(wǎng)友

an=[9^n(n +1)]/(10^n),a(n+1)/an=(9/10)[1+1/(n+1)],1.當(dāng)n9,1+1/(n+1)]a(n+1)/ann10, an10/9==a(n+1)/an1==當(dāng)nan.3.a8=a9.4.a10