# What would angle φ be?

Tags:
1. Nov 9, 2015

### aracali

1. The problem statement, all variables and given/known data
The mirror in the image below deflects a horizontal laser by angle θ. What is the angle φ if θ = 60°.

2. Relevant equations
θir

3. The attempt at a solution
So I know that, if I draw a line normal to the mirror, that will make it so that the incident angle and the reflected angle equal 60° (since 180-60=120 and the 2 angles have to be the same, so 120/2=60) but after that, I have no idea what to do. I know the angle is 30°, but how did they get that angle. Maybe I just need to reviw my geometry.

2. Nov 9, 2015

### Simon Bridge

Draw the normal to the mirror and identify the angle of incidence and the angle of reflection.
 ... also derive the equation rrlating the angles first, then plugbin the numbers

Take care with notation.

Last edited: Nov 10, 2015
3. Nov 9, 2015

### Staff: Mentor

Yes, you'll get nowhere without your junior high geometry. Relationships expressed concisely as "co-interior angles are supplementary", or maybe use "alternate angles are equal".