Mathematics - 3D-Coordinate Geometry Question with Solution | TestHub

The lines can be written as $\frac{x-b}{a}=\frac{y}{1}=\frac{z-d}{c}$ and $\frac{x-b^{\prime }}{a^{\prime }}=\frac{y}{1}=\frac{z-d^{\prime }}{c^{\prime }}$, which are perpendicular if and only if $a{a}^{\prime }+1+c{c}^{\prime }=0$.