Gọi A = 31 + 32 + 33 + 34 + .............................. + 32012
A = (31 + 32 + 33 + 34) + (35 + 36 + 37 + 38) + ................ + ( 32009 + 32010 + 32011 + 32012)
A = (3 + 9 + 27 + 81) + 34.(3 + 9 + 27 + 81) + ................. + 32008.(3 + 9 + 27 + 81)
A = 120 + 34 . 120 + ........................ + 32008.120
A = 120.(1 + 34 + .............. + 32008)
31+32+.... +32012
=( 31+32 +33+34)+(35+36+37+38)....+(32009+32010+32011+32012)
=120+31(3+31+32+33)+....+32008(3+31+32+33)
=120+31(120)+...32008(120)
=120(1+31+...+32012)
Suy ra tong chia het cho 120
dung 100% luon bai nay minh hoc roi
k minh nha
