Question

Let $L_1$ and $L_2$ are two intersecting lines.
If the image of $L_1$ w.r.t. $L_2$ and $L_2$ w.r.t. $L_1$
coincide, then angle between $L_1$ and $L_2$ is-

• A. ${35}^{\circ }$
• B. ${60}^{\circ }$
• C. ${90}^{\circ }$
• D. ${45}^{\circ }$

Answer 1

The correct option is B ${60}^{\circ }$

Let angle between $L_1$ and $L_2$ is $\theta$.

In diagram,
$L_1^{\prime }$ is image of $L_1$ w.r.t. to $L_2$ and
$L_2^{\prime }$ is image of $L_2$ w.r.t. to $L_1$.
If $L_1^{\prime }$ and $L_2^{\prime }$ are coinciding , then
angle between them i.e $3\theta ={180}^{\circ }$
$\Rightarrow \theta ={60}^{\circ }$