Question #46824

1 Answer
Oct 15, 2017

#90°#

Explanation:

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We know that the reflected ray from the mirror, the mirror and the horizontal will make a triangle.

Sum of angles of a triangle #=180°#

Let's call that triangle #∆ABC#

We know that #A= theta#

As #angle i =theta, angler=theta#

And, #angler +angleABC=90°#
[With the normal]

#therefore angle ABC+theta=90°#
#=>angleABC=90°-theta---(1)#

#angle ABC + theta + angle BCA = 180°#

We want to find #angleBCA#.

So, #angle BCA = 180°-(theta+angleABC)#

Substituting from (1),
#angle BCA = 180°-(cancel(theta)+90cancel(-theta))#

#therefore angleBCA=180-90=90°#

Since #angleBCA=90°#, the angle between the reflected ray and the horizontal would be #90°#