Question

what should be the angle between two plane mirror so that whatever be the angle of incidence , the incident ray and the reflected ray from the two mirror be parallel to each other​

Answer 1

Incident ray and finally reflected ray are parallel to each other means δ = 180∘

From δ=360−2θ⇒180=360−2θ⇒θ=90∘

Answer 2

$\huge\mathbb\purple{QUESTION}$

What should be the angle between two plane mirrors so that whatever be the angle of incidence,the incident ray and the reflected ray from the two mirrors be parallel to each other?

$\huge\mathbb\purple{ANSWER}$

When two plane mirrors, like A and B, are placed perpendicular to each other, the incident ray and reflected ray will always be parallel to each other, whatever may be the angle of incidence.

$\huge\mathbb\purple{EXPLANATION }$

See the attachment.

$\huge\mathbb\purple{HOPE \: IT\: HELPS.}$