Question

[Tran Khanh Ly]

CMR 12^1980-2^1000 chia het cho 10

19^1981+11^1980chia het cho 10

3+3^3+3^5+...+3^1991chia het cho 13

Answer 1

[✓ ℍɠŞ_ŦƦùM $₦G ✓]

A =19^1981+11^1980 

19^1981 = ( 2.10 -1)^1981 đồng dư -1 (mod 10) 

11^1980 = ( 10 +1)^1980 đồng dư 1 (mod 10) 

=> A chia hết cho 10.(dpcm)