Question

Cho A=2+2^2+2^3+.........+2^50

So sánh A với 2^51

Answer 1

2A=2²+2³+2⁴+...+2⁵⁰+2⁵¹

=> 2A-A=(2²+2³+2⁴+...+2⁵⁰+2⁵¹) -(2+2²+2³+2⁴+...+2⁵⁰)

<=> A=2⁵¹-2

=> A=2⁵¹-2<2⁵¹

Answer 2

2A=2²+2³+2⁴+...+2⁵⁰+2⁵¹

=>2A-A=( 2²+2³+2⁴+...+2⁵⁰+2⁵¹)-(2+2²+2³+2⁴+...+2⁵⁰)

óA=2⁵¹-2

=>A=2⁵¹-2<2⁵¹