Question

4+2²+2³+2⁴+.......+2^{20 làm như nào mọi người}

Answer 1

A=2²+2²+2³+2⁴+...+2²⁰

2A=2³+2³+2⁴+2⁵+...+2²¹

2A-A=A=2²¹+2³-2²-2²

A=2²¹+8-4-4

A=2²¹

Answer 2

A=2²+2²+2³+2⁴+...+2²⁰

2A=2³+2³+2⁴+2⁵+...+2²¹

2A-A=A=2²¹+2³-2²-2²

A=2²¹+8-4-4

A=2²¹

Answer 3

Đặt A = 4 + 2² + 2³ + 2⁴ +....+ 2²⁰ 

=> 2A = 8 + 2³ + 2⁴ + 2⁵ +....+ 2²¹ 

=> 2A - A = ( 8 + 2³ + 2⁴ + 2⁵ +....+ 2²¹ ) - (4 + 2² + 2³ + 2⁴ +....+ 2²⁰ )

=> A = 8 + 2²¹ - 4 + 2²

=> A = 4 + 2²¹ + 2²

=> A = 4 + 2097152 + 4 = 2097160

Answer 4

\(A=2^2+2^2+2^3+2^4+...+2^{20}\)

\(2A=2.\left(2^2+2^2+2^3+2^4+...+2^{20}\right)\)

\(2A=2^3+2^3+2^4+2^5+...+2^{21}\)

\(2A-A=\left(2^3+2^3+2^4+2^5+...+2^{21}\right)-\left(2^2+2^2+2^3+2^4+...+2^{21}\right)\)

\(A=2^{21}+2^3-2^2-2^2\)

\(A=2^{21}\)