Giải thích các bước giải:
$a)24=2^3.3$
$40=2^3.5$
$168=2^3.3.7$
$\text{$⇒$ BCNN$\{24;40;168\}=2^3.3.5.7=840$}$
$b)30=2.3.5$
$105=3.5.7$
$\text{$⇒$ BCNN$\{30;105\}=2.3.5.7=210$}$
$c)28=2^2.7$
$40=2^3.5$
$140=2^2.5.7$
$\text{$⇒$ BCNN$\{28;40;140\}=2^3.5.7=280$}$
$d)100=2^2.5^2$
$120=2^3.3.5$
$200=2^3.5^2$
$\text{$⇒$ BCNN$\{100;120;200\}=2^3.3.5^2=600$}$
$e)16=2^4$
$25=5^2$
$\text{$⇒$ BCNN$\{16;25\}=2^4.5^2=400$}$
Học tốt!!!