Bài 1:
BCNN(120,15,38)
Ta có: 120 = 23 . 3 . 5
15 = 3 . 5
38 = 2 . 19
~> BCNN(120,15,38) = 23 . 3 . 5 . 19 = 2280
BCNN(27,39,63)
Ta có: 27 = 33
39 = 3 . 13
63 = 32 . 7
~> BCNN(27,39,63) = 33 . 13 . 7 = 2457
1. BCNN(120,15,38)=2280
BCNN(27,39,63)=2457
Bài 1 :
\(120=2^3.3.5\\ 15=3.5\\ 38=2.19\\ \Rightarrow BCNN\left(120;15;38\right)=2^3.3.5.19=27.3.5.19=7695\\ 27=3^3\\ 39=3.13\\ 63=3^2.7\\ \Rightarrow BCNN\left(27;39;62=3\right)=3^3.7.13=2457\)
Bài 2:
a) Ta có: 60 = 22 . 3 . 5
280 = 23 . 5 . 7
~> BCNN(60,280) = 23 . 3 . 5 . 7 = 840
b) Ta có: 84 = 22 . 3 . 7
108 = 33 . 22
~> BCNN(84,108) = 33 . 22 . 7 = 756
c) Ta có: 13 = 13
15 = 3 . 5
~> BCNN(13,15) = 13 . 5 . 3 = 195
d) Ta có: 10 = 5 . 2
12 = 3 . 22
15 = 3 . 5
~> BCNN(10,12,15) = 5 . 22 . 3 = 60
e) Ta có: 8 = 23
9 = 32
11 = 11
~> BCNN(8,9,11) = 23 . 32 . 11 = 792
f) Ta có: 24 = 23 . 3
40 = 23 . 5
168 = 23 . 3 . 7
~> BCNN(24,40,168) = 23 . 5 . 7 . 3 = 840