Đáp án:
1 + 2 + 2² + 2³ + $2^{4}$ + $2^{5}$ + ..... + $2^{8}$ + $2^{9}$
= 3 + 2² + 2² . 2 + $2^{4}$ + $2^{4}$ . 2 + ..... + $2^{8}$ + $2^{8}$ . 2
= 3 + 2² . (1 + 2) + $2^{4}$ . (1 + 2) + ..... + $2^{8}$ . (1 + 2)
= 3 + 2² . 3 + $2^{4}$ . 3 + ..... + $2^{8}$ . 3 ⋮ 3
=> ĐPCM
Chúc học tốt!!!