hộ mình câu b thôi nhé hạn 2 h

Mình làm luôn cho bạn `2` câu nhé!
`a)S=2+2^2+2^3+2^4+2^5+2^6+2^7+2^8`
`S=(2+2^2)+(2^3+2^4)+(2^5+2^6)+(2^7+2^8)`
`S=1.(2+2^2)+2^2.(2+2^2)+2^4.(2+2^2)+2^6.(2+2^2)`
`S=1.6+2^2. 6+2^4. 6+2^6. 6`
`S=6.(1+2^2+2^4+2^6)`
Vì `6vdots-6`
`=>Svdots-6`
`b)S=3+3^2+3^3+3^4+3^5+3^6+3^7+3^8+3^9`
`S=(3+3^2+3^3)+(3^4+3^5+3^6)+(3^7+3^8+3^9)`
`S=1.(3+3^2+3^3)+3^3.(3+3^2+3^3)+3^6.(3+3^2+3^3)`
`S=1.39+3^3. 39+3^6. 39`
`S=39.(1+3^3+3^6)`
Vì `39vdots-39`
`=>Svdots-39`