1+3+9+27+81+.+6561=________

1+3+9+27+81+.+6561=________
1+3+9+27+81+.+6561=________

1+3+9+27+81+.+6561=________
1+3+9+27+81+243+729+2187+6561
=9 841
或者a1= 1 q=3
Tn= a1(1-q^n)/(1-q)
T9= (1-3^9) /(1-3)=9841

9841

1+3+9+27+81+......+6561=m
3+9+27+81+......+6561*3=3m
3m-m=6561*3-1
2m=19682
m=9841

等比数列求和Sn=a1(1-q^n)/(1-q) =(a1-an*q)/(1-q) (q≠1) ，a1=1，q=3，n=9自己算吧