Question

tính nhanH

 

a=3+3²⁺3³+.......+3¹⁰⁰

Answer 1

a=3+3^2+3^3+...+3^100

3a=3^2+3^3+3^4+...+3^101

3a-a=(3^2+3^3+3^4+...+3^101)-(3+3^2+3^3+...+3^100)

2a=3^101-3

2a=3^100

a=3^100/2

Answer 2

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

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

3A-A=3^101-3

2A=3^101-3

A=(3^101-3)÷2

Answer 3

3A=(3+3²⁺3³+.......+3¹⁰⁰)

3A=3²+3³+...+3¹⁰¹

3A-A=(3²+3³+...+3¹⁰¹)-(3+3²⁺3³+.......+3¹⁰⁰)

2A=3¹⁰¹-3

A=3¹⁰¹-3/2