i can't understand example 2 please explain me briefly  and fastt

Dear Student!

Here is the answer to your query.

Let us imagine AB acts as a mirror. Then P' is the position of image of point P.

Let us join P' and Q by a straight line which passes through the wall at point R.

Since the object and its mirror image are at the same distance from the mirror.

∴ P and P' are at the same distance from the wall 

⇒PR = P'R   ... (1)

Now the shortest distance between P' and Q is P'Q and P'Q = P'R + RQ

⇒ P'Q = PR + RQ   (From (1))

Hence the path from P to R and then from R to Q is the shortest path when should be followed by Sanjana.

Cheers!