Q86 / 160 · AP EAMCET 2019 (20 Apr Shift 2) · Mathematics
The straight line $x+y+1=0$ bisects an angle between a pair of lines, of which one is $2 x-3 y+4=0$. Then the equation of the other line in that pair is
- A$2 x+3 y+4=0$
- B$x-y+1=0$
- C$5 x-5 y+9=0$
- Correct answerD$3 x-2 y+5=0$
Solution
Point of intersection of lines $x+y+1=0$ and
$$
2 x-3 y+4=0 \text { is } A\left(-\frac{7}{5}, \frac{2}{5}\right) \text {. }
$$
Now, Let a point $P(-2,0)$ on the line $2 x-3 y+4=0$ and the image of point $P(-2,0)$ w.r.t. line $x+y+1=0$ lying on the other line in the bisector pair. If the coordinate of image of point $P(-2,0)$ w.r.t. line $x+y+1=0$ is $(h, k)$, then
$$
\begin{array}{ll}
\frac{h+2}{1}=\frac{k-0}{1}=-2 \times \frac{-2+1}{2}=1 \\
\Rightarrow \quad h=-1 \text { and } k=1 \\
\Rightarrow \quad & (h, k)=(-1,1)
\end{array}
$$
Now, equation of required bisector of angle is line joining the points $A\left(-\frac{7}{5}, \frac{2}{5}\right)$ and $(-1,1)$ is
$$
\begin{gathered}
y-1=\frac{\frac{3}{5}}{\frac{2}{5}}(x+1) \Rightarrow 2 y-2=3 x+3 \\
3 x-2 y+5=0
\end{gathered}
$$
Hence, option (d) is correct.
Hence, the correct answer is option: 'D'.