vì 72 chia hết 36 và 18
=>UCLN(18,36,72) là 72
\(40=2^3.5\)
\(75=5^3\)
\(105=5.3.7\)
\(ƯCLN\)\(\left(40;75;105\right)=5\)
\(BCNN\)\(\left(40;75;105\right)=5^3.2^3.3.7=21000\)
---------------------------------------------------------------------------------------
\(18=2.3^2\)
\(36=2^2.3^2\)
\(72=2^3.3^2\)
\(ƯCLN\)\(\left(18;36;72\right)\)\(=2.3^2=18\)
\(BCNN\)\(\left(18;36;72\right)=2^3.3^2=72\)