How Does Light Refract Through a Prism with Different Angles?

[StumpedFrosh]

Homework Statement

Light is incident on a glass prism with an angle of incidence of 54°. The light enters on the left hand side of a triangular prism with base angles of 80° and apex angle of 20°. (The 54° ray of incidence enters from the south west side of the prism, directed towards the north east). Calculate all the angles as a ray of light travels through a prism. Assume that the prism is surrounded with air therefore n=1, also the n value of the prism is n=1.7.

Homework Equations

snell's law: n1sinΘ1=n2sinΘ2

The Attempt at a Solution

With the given information i drew the image and determined through snell's law that the first angle of refraction (Θ2) equals 28.4°... I don't understand how to find Θ3.

 

[Simon Bridge]

You have to use you knowledge of triangles and angles to work out an incident angle to the second side.
Since you have a sketch, you can continue the ray into the prism until it strikes the other side.
The ray and the apex of the prism will make a triangle where you know two of the angles.