Question

cho A=2+2^2+2^3+...+2^60

CMR: A chia hết cho 15

Answer 1

A=2+2^2+2^3+...+2^60

A=(2+2^2+2^3+2^4)+....+(2^57+2^58+2^59+2^60)

A=15.2^0+....+15.2^56

A=15.(2^0+2^4+...+2^56) chia hết cho 15

Vậy A chia hết cho 15