E= 1+3+3^2+3^3 +... + 3^119 chia hết cho 13
Giải thích
E=1+3+32+33+...+3119 chia hết cho 13
E=1+3+32+33.1+3+32+...+3117.1+3+32
E=13+33.13+...+3117.13
E=13.1+33+...+3117⋮13đpcm
E=1+3+32+33+...+3119 chia hết cho 13
E=1+3+32+33.1+3+32+...+3117.1+3+32
E=13+33.13+...+3117.13
E=13.1+33+...+3117⋮13đpcm