4+5+7+4+2+4+4+9=39
co to day
4 + 5 + 7 + 4 + 2 + 4 + 4 + 9 = 9 + 11 + 6 + 15 = 20 + 21 = 41
có nhé
4+5+7+4+2+4+4+9
=4x4+5x1+7x1+2x1+9x1
=16+5+7+2+9
21+7+2+9
=28+2+9
=30+9
39
\(4+5+7+4+2+4+4+9\)
=\(\left(4+5\right)+\left(7+2\right)+\left(4.3\right)+9\)
=\(9+9+12+9\)
=\(9.3+12=27+12=39\)