A person standing at the junction (crossing) of two straight paths represented by the equations 2x – 3y + 4 = 0 and 3x + 4y – 5 = 0 wants to reach the path whose equation is 6x – 7y + 8 = 0 in the least time. Find equation of the path that he should follow.
The equations of the given lines are
2x – 3y + 4 = 0 … (1)
3x + 4y – 5 = 0 … (2)
6x – 7y + 8 = 0 … (3)
The person is standing at the junction of the paths represented by lines (1) and (2).
On solving equations $(1)$ and $(2)$, we obtain $x=-\frac{1}{17}$ and $y=\frac{22}{17}$.
Thus, the person is standing at point $\left(-\frac{1}{17}, \frac{22}{17}\right)$.
The person can reach path $(3)$ in the least time if he walks along the perpendicular line to $(3)$ from point $\left(-\frac{1}{17}, \frac{22}{17}\right)$
Slope of the line $(3)=\frac{6}{7}$
$\therefore$ Slope of the line perpendicular to line $(3)=-\frac{1}{\left(\frac{6}{7}\right)}=-\frac{7}{6}$
The equation of the line passing through $\left(-\frac{1}{17}, \frac{22}{17}\right)$ and having a slope of $-\frac{7}{6}$ is given by
$\left(y-\frac{22}{17}\right)=-\frac{7}{6}\left(x+\frac{1}{17}\right)$
$6(17 y-22)=-7(17 x+1)$
$102 y-132=-119 x-7$
$119 x+102 y=125$
Hence, the path that the person should follow is $119 x+102 y=125$.