Question

CMR: 2+2^2+2^3+...+2^99+2^100 phải chia hết cho 3

Answer 1

A=2+2^2+2^3+...+2^99+2^100
A= 2.(1+2)+2^3(1+2)+....+2^99.(1+2)
A= 2.3+2^3.3+...2^99.3
A= 3.(2+2^3+..+2^99)
vậy A chia hết cho 3