Question

A=2+2^2+2^3+2^4+...+2^2010.CMR :Achia hết cho 3 và 7

Answer 1

A= (2+2^2)+(2^3+2^4)+(2^5+2^6)+.....+(2^59+2^60) = 2.(1+2)+2^3.(1+2)+.....+2^59.(1+2) = (2+2^3+...+2^59).3 chia hết cho 3 A=(2+2^2+2^3)+(2^4+2^5+2^6)+....+(2^58+2^59+2^60) = (2+2^4+...+2^58).(1+2+2^2) =_______________.7 chia hết cho 7

Answer 2

De chung minh A chia het cho 3 thi ta co nhom nhu sau :