Question

A=1+3+3^2+3^3+3^4+....+3^11

tìm 2A biết 2A+3=A

Answer 1

A=1+3+3²+3³+3⁴+....+3¹¹

3A=3(1+3+3²+3³+3⁴+....+3¹¹) 

3A=3+3²+3³+3⁴+3⁵+....+3¹²

3A-A=(3+3²+3³+3⁴+3⁵+....+3¹²)-(1+3+3²+3³+3⁴+....+3¹¹)

2A=3¹²-1

A=3¹²-1+3

A=3¹²+2

A=531443

Answer 2

Ta có:

A=1+3+...+3^11

\(\Rightarrow\)3A=3+3^2+3^3+...+3^12

3A-A=3+3^2+...+3^12-1-3-3^2-...-3^11

2A=3^12-1=531441-1=531440

Answer 3

Ta c c pop 1+3+....+3^11

=>3A=3+3^2+...3^12

3A-A=lay cai tren - de bai

1A=531440