9+9+9+9+9+1+2+3+4+5+6+7+8
= 9 x 5 + 36
= 45 + 36 =
= 81
9 + 9 + 9 + 9 + 9 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 81
9 + 9 + 9 + 9 + 9 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 81
9 + 9 + 9 + 9 + 9 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8
=9 x 5 + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + 1 + 5
= 45 + 10 + 10 + 10 + 6
=81 nha
9 + 9 + 9 + 9 + 9 + 1 + 2 + 3 + 4 + 5 + 6 +7 + 8 = 81
9+9+9+9+9+1+2+3+4+5+6+7+8
=9 x 5 + 36
=45 +36
=81