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Question: Answered & Verified by Expert
$\mathrm{B}(2,3), \mathrm{C}(5,-2) . \mathrm{D}(1,-1)$ are three points. If $\mathrm{A}$ is a variable point such that the area of the quadrilateral $\mathrm{ABCD}$ is $10 \mathrm{sq}$. units, then the locus of $\mathrm{A}$ is
MathematicsStraight LinesTS EAMCETTS EAMCET 2022 (20 Jul Shift 1)
Options:
  • A $(x-4 y+42)(x-4 y+2)=0$
  • B $(x-4 y-42)(x-4 y-2)=0$
  • C $(4 x-y+42)(4 x-y+2)=0$
  • D $(4 x-y-42)(4 x-y-2)=0$
Solution:
2431 Upvotes Verified Answer
The correct answer is: $(4 x-y-42)(4 x-y-2)=0$
Given vertices of quadrilateral $\mathrm{ABCD}$ are $\mathrm{B}(2,3)$ $\mathrm{C}(5,-2)$ and $\mathrm{D}(1,-1)$ with area of $\mathrm{ABCD}$ is 10 sq. units.
Area of quadrilateral $\mathrm{ABCD}=$
$$
\pm \frac{1}{2}\left\{\left(\mathrm{x}_1-\mathrm{x}_3\right)\left(\mathrm{y}_2-\mathrm{y}_1\right)-\left(\mathrm{x}_2-\mathrm{x}_4\right)\left(\mathrm{y}_1-\mathrm{y}_3\right)\right\}
$$
Let the vertex $A$ is $(x, y)$
Area of quadrilateral $\mathrm{ABCD}=$
$$
\begin{aligned}
& \pm \frac{1}{2}\{(\mathrm{x}-5)(3+1)-(2-1)(\mathrm{y}+2)\} \\
& 10=\frac{1}{2}\{4(\mathrm{x}-5)-(\mathrm{y}+2)\} \\
& 4 \mathrm{x}-20-\mathrm{y}-2=20 \\
& 4 \mathrm{x}-\mathrm{y}-22=20 \\
& 4 \mathrm{x}-\mathrm{y}-42=0
\end{aligned}
$$
Also, $10=-\frac{1}{2}\{4(\mathrm{x}-5)-(\mathrm{y}+2)\}$
$$
\begin{aligned}
& 20=-\{4 x-20-y-2\} \\
& 20=-\{4 x-y-22\}
\end{aligned}
$$
$$
\begin{aligned}
& 4 x-y-22=-20 \\
& 4 x-y-2=0
\end{aligned}
$$
Locus of point $A$ is $(4 x-y-42)(4 x-y-2)=0$ So,option (d) is correct.

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