$Bài$ $2$
a) $30= 2^{2} . 5$
$25=5^{2}$
$75=5^{3}$
⇒$BCNN$ (30 , 25 , 75) = $2^{2}$ . $5^{3}$ = 500
b) $15=5.3$
$40=2^{3}.5 $
$120=2^{4} .5$
⇒$BCNN(15 , 40 , 120)=2^{4}.3.5=240$
c) $13=13$
$17=17$
$21=3.7$
⇒$BCNN(13 , 17 , 21)=13.7.3.17=4641$
d) $21=3.7$
$15=5.3$
$65=.5^{2}.3$
⇒$BCNN(21 , 15 , 65)=3.5^{2}.7=1365$
$Cho$ $mk$
5 sao + câu trả lời hay nhất + cảm ơn nha !