If $2 x+3 y=5$ is the perpendicular bisector of the line segment joining the points $A\left(1,…

If $2 x+3 y=5$ is the perpendicular bisector of the line segment joining the points $A\left(1, \frac{1}{3}\right)$ and $B$, then $B$ is equal to
  1. $\left(\frac{21}{13}, \frac{49}{39}\right)$
  2. $\left(\frac{17}{13}, \frac{31}{39}\right)$
  3. $\left(\frac{7}{13}, \frac{49}{39}\right)$
  4. $\left(\frac{21}{13}, \frac{31}{39}\right)$

Solution

Let $\quad l_1 \equiv 2 x+3 y=5$ Since, line $A B \perp I_1$ $\therefore$ Slope of $l_1$ is $ \begin{array}{r} m_1 \text { say }=\frac{-2}{3} \\ \therefore \text { Slope of } A B=\frac{-1}{(-2 / 3)}=\frac{3}{2} \end{array} $
Equation of line $A B$ is $ \begin{array}{cc} & \left(y-\frac{1}{3}\right)=\frac{3}{2}(x-1) \\ \Rightarrow \quad & 3 x-2 y=\frac{7}{3} \end{array} $ Equation of line $I_1$ is $ 2 x+3 y=5 $ From Eqs. (i) and (ii), we get $ \Rightarrow \quad \begin{array}{rl} 13 x & =17 \\ x & x=\frac{17}{13} \end{array} $ From Eq. (i), we get $ 3 y=5-\frac{34}{13} \Rightarrow y=\frac{65-34}{13 \times 3}=\frac{31}{39} $ So, mid-point $P \rightarrow\left(\frac{17}{13}, \frac{31}{39}\right)$ Coordinate of point $B$ $ \begin{aligned} & =\left(\frac{17}{13} \times 2-1, \frac{31}{39} \times 2-\frac{1}{3}\right) \\ & =\left(\frac{34-13}{13}, \frac{62-13}{39}\right)=\left(\frac{21}{13}, \frac{49}{39}\right) \end{aligned} $

Asked in: AP EAMCET 2013

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