Do the following equations represent a pair of coincident lines? Justify your answer.
(i) $3 x+\frac{1}{7} y=3$ and $7 x+3 y=7$
(ii) $-2 x-3 y=1$ and $6 y+4 x=-2$
(iii) $\frac{x}{2}+y+\frac{2}{5}=0$ and $4 x+8 y+\frac{5}{16}=0$
Condition for coincident lines,
$\frac{a_{1}}{a_{2}}=\frac{b_{1}}{b_{2}}=\frac{c_{1}}{c_{2}}$
(i) No, given pair of linear equations
$3 x+\frac{y}{7}-3=0$
and $\quad 7 x+3 y-7=0$,
where, $\quad a_{1}=3, b_{1}=\frac{1}{7}, c_{1}=-3$;
$a_{2}=7, b_{2}=3, c_{2}=-7$
Now, $\frac{a_{1}}{a_{2}}=\frac{3}{7}, \frac{b_{1}}{b_{2}}=\frac{1}{21}, \frac{c_{1}}{c_{2}}=\frac{3}{7}$ $\left[\because \frac{a_{1}}{a_{2}} \neq \frac{b_{1}}{b_{2}}\right]$
Hence, the given pair of linear equations has unique solution.
(ii) Yes, given pair of linear equations
$-2 x-3 y-1=0$ and $6 y+4 x+2=0$
where, $a_{1}=-2, b_{1}=-3, c_{1}=-1$
$a_{2}=4, b_{2}=6, c_{2}=2$
Now, $\frac{a_{1}}{a_{2}}=-\frac{2}{4}=-\frac{1}{2}$
$\frac{b_{1}}{b_{2}}=-\frac{3}{6}=-\frac{1}{2}, \frac{c_{1}}{c_{2}}=-\frac{1}{2}$
$\because$ $\frac{a_{1}}{a_{2}}=\frac{b_{1}}{b_{2}}=\frac{c_{1}}{c_{2}}=-\frac{1}{2}$
Hence, the given pair of linear equations is coincident.
(iii) No, the given pair of linear equations are
$\frac{x}{2}+y+\frac{2}{5}=0$ and $4 x+8 y+\frac{5}{16}=0$
Here, $a_{1}=\frac{1}{2}, b_{1}=1, c_{1}=\frac{2}{5}$
$a_{2}=4, b_{2}=8, c_{2}=\frac{5}{16}$
Now, $\frac{a_{1}}{a_{2}}=\frac{1}{8}, \frac{b_{1}}{b_{2}}=\frac{1}{8}, \frac{c_{1}}{c_{2}}=\frac{32}{25}$
$\because$ $\frac{a_{1}}{a_{2}}=\frac{b_{1}}{b_{2}} \neq \frac{c_{1}}{c_{2}}$
Hence, the given pair of linear equations has no solution.