Question

a.A = 1 + 3 + 3²+ ...+ 3¹¹chia hết cho 4

Answer 1

`1+3+3^2+...+3^11`
`=3+1+3^2(1+3)+......+3^10(3+1)`
`=(3+1)(1+3^2+...+3^10)`
`=4(1+3^2+...+3^10) \vdots 4(đpcm)`

Answer 2

`A=(1+3+3^2+3^3+3^4)+....+(....+3^11)`

`=40+3^4 .40 + 3^8 .40`

`=40.(1+3^4+3^8)`

`=4.10 (1+3^4+3^8) ⋮ 4`.

Answer 3

Giải:

A=1+3+3²+...+3¹¹

A=1.(1+3)+3².(1+3)+3⁴.(1+3)+...+3¹⁰.(1+3)

A=(1+3).(1+3²+3⁴+...+3¹¹)

A=4.(1+3²+3⁴+...+3¹⁰) ⋮ 4 (đpcm) 

Chúc bạn học tốt!

Answer 4

a) Ta có: \(A=1+3+3^2+...+3^{11}\)

\(=\left(1+3\right)+\left(3^2+3^3\right)+...+\left(3^{10}+3^{11}\right)\)

\(=4+3^2\cdot4+...+3^{10}\cdot4\)

\(=4\left(1+3^2+...+3^{10}\right)⋮4\)(đpcm)