Lời giải:
$S=4+12+36+108+....+972+2916$
$3\times S=12+36+108+324+...+2916+8748$
$3\times S-S=(12+36+108+324+...+2916+8748)-(4+12+36+108+....+972+2916)$
$2\times S=8748-4=8744$
$S=8744:2=4372$
Đúng 1
Bình luận (0)