Theo đề, ta có:
\(a⋮12\) \(;\) \(a⋮25\) \(;\) \(a⋮30\) \(\Rightarrow\) \(a\in BC\left(12;25;30\right)\)
\(12\) = \(2^2.3\)
25 = \(5^2\)
30 = \(2.3.5\)
\(\Rightarrow BCNN\left(12;25;30\right)=2^2.3.5^2=300\)
\(\Rightarrow BC\left(12;25;30\right)=\left\{0;300;600;...\right\}\)
Vì 0 < a < 500
\(\Rightarrow a=300\)
\(a⋮12\)
\(a⋮25\) \(\Rightarrow a\in BC\left(12;25;30\right)\)
\(a⋮30\)
\(12=2^2.3\)
\(25=5^2\)
\(30=2.3.5\)
\(BCNN\left(12;25;30\right)=2^2.3.5^2=300\)
\(BC\left(12;25;30\right)=b\left(300\right)\)
\(B\left(300\right)=\left\{0;300;600;.......\right\}\)
\(0< a< 500\)
\(\Rightarrow a=300\)
\(\left\{{}\begin{matrix}a⋮12\\a⋮25\\a⋮30\end{matrix}\right.\Leftrightarrow a\inƯC\left(12;25;30\right)}\)
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