B=1/3+1/9+1/27+…+1/2187+1/6561 giải hộ mình với,mình đg cần gấp 02/09/2021 Bởi Reese B=1/3+1/9+1/27+…+1/2187+1/6561 giải hộ mình với,mình đg cần gấp
`B=1/3+1/9+1/27+…+1/2187+1/6561` `B=1/3+1/3^2+1/3^3+…+1/3^6+1/3^7` `3B=3(1/3^1+1/3^2+1/3^3+…+1/3^6+1/3^7)` `3B=1+1/3+1/3^2+…+1/3^5+1/3^6` `3B-B=(1+1/3+1/3^2+…+1/3^5+1/3^6)-(1/3+1/3^2+1/3^3+…+1/3^6+1/3^7)` `2B=1+1/3+1/3^2+…+1/3^5+1/3^6-1/3-1/3^2-1/3^3-…-1/3^6-1/3^7` `2B=1-1/3^7` `2B=(3^7+1)/3^7` `B=((3^7+1)/3^7):2` Bình luận
`B=1/3+1/9+1/27+…+1/2187+1/6561`
`B=1/3+1/3^2+1/3^3+…+1/3^6+1/3^7`
`3B=3(1/3^1+1/3^2+1/3^3+…+1/3^6+1/3^7)`
`3B=1+1/3+1/3^2+…+1/3^5+1/3^6`
`3B-B=(1+1/3+1/3^2+…+1/3^5+1/3^6)-(1/3+1/3^2+1/3^3+…+1/3^6+1/3^7)`
`2B=1+1/3+1/3^2+…+1/3^5+1/3^6-1/3-1/3^2-1/3^3-…-1/3^6-1/3^7`
`2B=1-1/3^7`
`2B=(3^7+1)/3^7`
`B=((3^7+1)/3^7):2`