5. Two plane mirrors are inclined at $70^◦$ . A ray incident on one mirror at angle θ after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of θ is ?

5. Two plane mirrors are inclined at $70^◦$ . A ray incident on one mirror at angle θ after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of θ is ?

(a) 50°

(b) 45°

(c) 30°

(d) 55°

Answer :  (a) 50°

\( 70^\circ + 90^\circ - x = 90^\circ \)

\( x = 70^\circ \)

\( 90^\circ - \theta + 70^\circ + 70^\circ = 180^\circ \)

\( 90^\circ - \theta = 40^\circ \)

\( \theta = 50^\circ \)