Find the equation of a straight line passing through the point of intersection of x + 2y + 3 = 0 and 3x + 4y + 7 = 0 and perpendicular to the straight line x – y + 9 = 0.
Find the equation of a straight line passing through the point of intersection of x + 2y + 3 = 0 and 3x + 4y + 7 = 0 and perpendicular to the straight line x – y + 9 = 0.

    \[x\text{ }+\text{ }2y\text{ }+\text{ }3\text{ }=\text{ }0\text{ }and\text{ }3x\text{ }+\text{ }4y\text{ }+\text{ }7\text{ }=\text{ }0\]

The equation of the straight line passing through the points of intersection of x + 2y + 3 = 0 and 3x + 4y + 7 = 0 is

    \[\begin{array}{*{35}{l}} x\text{ }+\text{ }2y\text{ }+\text{ }3\text{ }+~\lambda \left( 3x\text{ }+\text{ }4y\text{ }+\text{ }7 \right)\text{ }=\text{ }0  \\ \left( 1\text{ }+\text{ }3\lambda  \right)x\text{ }+\text{ }\left( 2\text{ }+\text{ }4\lambda  \right)y\text{ }+\text{ }3\text{ }+\text{ }7\lambda ~=\text{ }0  \\ \end{array}\]

RD Sharma Solutions for Class 11 Maths Chapter 23 – The Straight Lines - image 107

The required line is perpendicular to x − y + 9 = 0 or, y = x + 9