a,Ta thấy :
\(\left\{{}\begin{matrix}60=2^2.3.5\\280=2^3.5.7\end{matrix}\right.\)
=> \(BCNN\left(60;280\right)=2^3.3.5.7=840\)
b,Ta thấy
\(\left\{{}\begin{matrix}84=2^2.3.7\\108=2^2.3^32^{ }\end{matrix}\right.\)
=> \(BCNN\left(84;108\right)=2^2.3^3.7=756\)
\(\)c, Ta thấy
\(\left\{{}\begin{matrix}13=13\\15=3.5\end{matrix}\right.\)
=> \(BCNN\left(13;15\right)=13.3.5=195\)