a1+3a2+3²a3+.+3的n-1次方 an=n/3 a1+3a2+3²a3+.+3的n-2次方 a(n-1)=(n-1)/3 n≥2两式相减3的n-1次方 an = 1/3an=1/(3^n)n=1时,带入a1+3a2+3²a3+.+3的n-1次方 an=n/3 a1=1/3满足an=1/(3^n)故an=1/(3^...