The pair of equations $a x+2 y=9$ and $3 x+$ by $=18$ represent parallel lines, where $a, b$ are int

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The pair of equations $a x+2 y=9$ and $3 x+$ by $=18$ represent parallel lines, where $a, b$ are integers, if :\

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(d) : The pair of equations $a x+2 y=9$ and $3 x+b y=18$ respectively are parallel lines when\ $\frac{a_{1}}{a_{2}}=\frac{b_{1}}{b_{2}} 
eq \frac{c_{1}}{c_{2}}$\ Here, $a_{1}=a, b_{1}=2, c_{1}=9$ and $a_{2}=3, b_{2}=b, c_{2}=18$\ $\Rightarrow \quad \frac{a}{3}=\frac{2}{b} 
eq \frac{9}{18}$\ $	herefore a b=6$