Question

Cho A = 1+2+2²+2³+2⁴+....+2²⁹

B = 2³⁰ - 1.

So sánh A và B

 

Answer 1

A=1+2+2²+...+2²⁹

2A=2+2²+2³+...+2³⁰

2A-A=(2+2²+2³+...+2³⁰)-(1+2+2²+...+2²⁹)

A=2³⁰-1

Vậy A=B

Answer 2

2A=2+2²+2³+2⁴+...+2³⁰

2A-A=2³⁰-1

suy ra: A=2³⁰-1 

suy ra A=B