Question

cho A=3^1+3^2+^3+..........+3^200.hãy tìm so tu nhien x de 2A+3=3x

Answer 1

Ta có

\(3A=3^2+3^3+....+3^{201}\)

\(\Rightarrow3A-A=2A=\left(3^2+3^3+....+3^{201}\right)-\left(3+3^2+....+3^{200}\right)\)

\(\Rightarrow2A=3^{201}-3\)

\(\Rightarrow2A-3=3^{201}\)

Mà 2A - 3= 3x

=>x=3²⁰⁰

Answer 2

3a=3²+3³+...+3²⁰¹

3a-a=2a= (3^2+3^3+...+3^201)-(3+3^2+...+3^201)

2a =3^201 -3

2a-3 =3^201

=>x= 3^200