Sửa đề: `N=1+3+3^2+3^3+...+3^100`
`text{Đáp án + Giải thích các bước giải}`
`text{_________________________________________________}`
`text{Ta có:}`
`N=1+3+3^2+3^3+...+3^100
`=>3N=3+3^2+3^3+3^4+...3^101`
`3N-N=3+3^2+3^4+3^6+...3^101 -1-3-3^2-3^3-...-3^100`
`2N=3^101-1`
`=>N=(3^101-1)/2`
`text{__________________________________________________}`
`text{Ta có:}`
`P=1+5^3+5^6+...+5^99`
`5^3 P=5^3+5^6+5^9+...+5^102`
`5^3 P-P=5^3+5^6+5^9+...+5^102-1-5^3-5^6-...-5^99`
`=>124P=5^102-1`
`=>P=(5^102-1)/124`
