I'm stuck at proving:
Let $a, b, c \in \mathbb{Z}, a\cdot b \neq 0$. Prove:
$$
a \mid m \hspace{15px}\text{and}\hspace{15px} b \mid m \implies \frac{a \cdot b}{\text{gcd}(a, b)} \mid m
$$
My current attempt looks like this:
Let $t := \text{gcd}(a, b)$ donate the greatest common divisor of $a$ and $b$.
$$
\implies\exists\, a', b': a = t\cdot a' \hspace{15px}\text{and}\hspace{15px} b = t \cdot b'
$$
$$
\implies \frac{a b}{\text{gcd}(a, b)} = \frac{a b}{t} = \frac{t a'b}{t} = a' b
$$
I know that since b \mid m: $a'b \mid m$ iff $\text{gcd}(a', b) = 1$ and $a' \mid m$, but I'm not sure whether this is the right approach to this problem.
Currently I don't know about identities involving the least common multiple.
Answer
By Bézout's lemma, there are integers $k$ and $l$ such that $\gcd(a,b)=ka+lb$. Therefore, $\gcd(a,b)m=kam+lbm$. Since $a\mid m$, $ab\mid lbm$ and since $b\mid m$, $ab\mid kam$. So, $ab\mid kam+lbm=\gcd(a,b)m$ and, since $\gcd(a,b)\mid ab$,$$ab\mid\gcd(a,b)m\iff\frac{ab}{\gcd(a,b)}\mid m.$$
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