Giải:
A=3+3^2+3^3+...+3^100
3A=3^2+3^3+3^4+...+3^101
3A-A=(3^2+3^3+3^4+...+3^101)-(3+3^2+3^3+...+3^100)
2A=3^101-3
A=(3^101-3):2
Tính tổng:
A=3^1+3^2+3^3+...+3^100
A=3(1+2+3+4+...+99+100)
A=3(100+1)x100:2
A=3101x100:2
A=310100:2
A=35050