Question

Tính A=2+2^2+2^3+...+2^10

Answer 1

Ta có: A = 2+2²+2³+...+2¹⁰

=> 2A = 2²+2³+2⁴+...+2¹¹

=> 2A - A = (2²+2³+...+2¹¹)-(2+2²+2³+...+2¹⁰)

=> A         = 2¹¹ - 2

Vậy A = 2¹¹ - 2

Answer 2

A = 2 + 2² + 2³ + ... + 2¹⁰

2A = 2 . ( 2 + 2² + 2³ + ... + 2¹⁰ )

2A = 2² + 2³ + 2⁴ + ... + 2¹¹

2A - A = ( 2² + 2³ + 2⁴ + ... + 2¹¹ ) - ( 2 + 2² + 2³ + ... + 2¹⁰ )

A = 2¹¹ - 2