Question

cho A=2+2^2+2^3+2^4+...............+2^100.chung minh Achia het cho 5

Answer 1

A = 2 + 2^2 + 2^3 + 2^4 + ... + 2^100.

2A = 2^1 + 2^2 + 2^3 + 2^4 + ... + 2^100 

2A - A = ( 2^1 + 2^2 + 2^3 + 2^4 + ... + 2^101 ) - ( 2 + 2^2 + 2^3 + 2^4 + ... + 2^100 )

1A = 2^100 - 1 chia hết cho 5

Answer 2

Cho A=2+2^2+2^3+2^4+...............+2^100.Chứng minh A chia hết cho 5

tớ làm giống Kirito :

A = 2 + 2^2 + 2^3 + 2^4 + ... + 2^100.

2A = 2^1 + 2^2 + 2^3 + 2^4 + ... + 2^100 

2A - A = ( 2^1 + 2^2 + 2^3 + 2^4 + ... + 2^101 ) - ( 2 + 2^2 + 2^3 + 2^4 + ... + 2^100 )

1A = 2^100 - 1 chia hết cho 5

nhé !