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Question: Answered & Verified by Expert
Joint equation of pair of lines through $(3,-2)$ and parallel to $x^{2}-4 x y+3 y^{2}=0$ is
MathematicsPair of LinesMHT CETMHT CET 2009
Options:
  • A $x^{2}+3 y^{2}-4 x y-14 x+24 y+45=0$
  • B $x^{2}+3 y^{2}+4 x y-14 x+24 y+45=0$
  • C $x^{2}+3 y^{2}+4 x y-14 x+24 y-45=0$
  • D $x^{2}+3 y^{2}+4 x y-14 x-24 y-45=0$
Solution:
2230 Upvotes Verified Answer
The correct answer is: $x^{2}+3 y^{2}-4 x y-14 x+24 y+45=0$
Given equation of line is $x^{2}-4 x y+3 y^{2}=0$ $\therefore m_{1}+m_{2}=\frac{4}{3}$ and $m_{1} m_{2}=\frac{1}{3}$
On solving these equations, we get $m_{1}=1, m_{2}=\frac{1}{3}$
Let the lines parallel to given line are $y=m_{1} x+c_{1}$ and $y=m_{2} x+c_{2}$
$\therefore$
$y=\frac{1}{3} x+c_{1}$ and $y=x+c_{2}$
Also, these lines passes through the point $(3,-2)$
$\therefore$
$-2=\frac{1}{3} \times 3+c_{1}$
$\Rightarrow \quad c_{1}=-3$
and $\quad-2=1 \times 3+c_{2}$
$\Rightarrow \quad c_{2}=-5$
$\therefore$ Required equation of pair of lines is $(3 y-x+9)(y-x+5)=0$
$\Rightarrow x^{2}+3 y^{2}-4 x y-14 x+24 y+45=0$

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