A=1+1+3+3^2+3^3+...+3^2018

A=1+(1+3+3^2+3^3+...+3^2018)

Đặt:

B=1+3+3^2+3^3+...+3^2018

3B=3.(1+3+3^2+3^3+...+3^2018)

3B=3+3^2+3^3+...+3^2018+3^2019

3B=1+3^2+3^3+...+3^2018+3^2019-1

3B=B+3^2019-1

3B-B=B+3^2019-1-B

2B=3^2019-1

=>2A=2B+1

=3^2019-1+1

=3^2019

2A-1

=3^2019-1

=3^n-1

3^n-1=3^2019-1

=>n=2019

Vậy n=2019

nhanh tích cho nhee

tui làm b nha do a không biết làm

A=5+3²+3³+...+3²⁰¹⁸

3A=15+3³+3⁴+...+3²⁰¹⁹

3A-A=(15+3³+3⁴+...+3²⁰¹⁹)-(5+3²+3³+...+3²⁰¹⁸)

2A=3²⁰¹⁹+15-(5+3²)

2A=3²⁰¹⁹+15-14

2A=3²⁰¹⁹+1

2A-1=3²⁰¹⁹+1-1

2A-1=3²⁰¹⁹

vậy n = 2019

cmon nhaa, mỗi câu b thoi cx đc :3

3A = 3 + 3^2 + 3^3 + .. + 3^100+ 3^101

A = 1 + 3 + 3^2 + .. + 3^100 

3A - A = 3 + 3^2 + 3^3 + .. + 3^100 + 3^101 - 1 - 3 - 3^2 - ... - 3^100

           = 3^101 - 1

2A = 3^101 - 1 

2A + 3 = 3^101 - 1 + 3 = 3^ 101 + 2 khác 3^n 

=> không có n thỏa mãn 

Ta có: A=1+3+3²+…+3¹⁰⁰

=>A.3=3+3²+3³+…+3¹⁰¹

=>A.3-A=3+3²+3³+…+3¹⁰¹-1-3-3²-…-3¹⁰⁰

=>A.2=3¹⁰¹-1

=>A.2+1=3¹⁰¹=3ⁿ

=>3¹⁰¹=3ⁿ

=>n=101

Vậy n=101

\(A=5+3^2+3^3+...+3^{2018}\)

\(3A=15+3^3+3^4+...+3^{2019}\)

\(3A-A=\left(15+3^3+3^4+...+3^{2019}\right)-\left(5+3^2+3^3+...+3^{2018}\right)\)

\(2A=1+3^{2019}\)

\(2A-1=3^{2019}\)

Suy ra \(n=2019\).