[tex]\it a\in M_{30},\ a\ne 0\\ \\ Pentru\ a\ =30,\ se\ ob\c{\it t}ine:\\ \\ 30\cdot\dfrac{-7}{3}=-\dfrac{210}{3}=-70 \in\mathbb{Z}\\ \\ \\ 30\cdot\dfrac{5}{-2}=-\dfrac{150}{2}=-75 \in\mathbb{Z}\\ \\ \\ 30\cdot\dfrac{-17}{15}=-\dfrac{510}{15}=-34 \in\mathbb{Z}[/tex]
