In Fig., when mirror is turned from position `M_1` to position `M_2` through `/_theta = 3.5^@`, the reflected ray turns through

`/_2 theta = 7^@ = /_AOB`

`OA = d = 1.5 m`

Displacement, `AB = x = ?`

In `Delta AOB tan 2 theta = (x)/(d)`

`x = d tan 2 theta = 1.5 tan 7^@ = 1.5 xx 0.1228`

=`0.18 metre`.

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