Plotting reflection coefficient

[nmsurobert]

Homework Statement

plot the magnitude |r| of the reflection coefficient as a function of incident angle from 0 to 90 degrees with a step size of 1 degree for the following cases: (ill only post one)

A transverse electric plane wave in incident from air to glass

Homework Equations

r = (n₁cosθ_i - n₂cosθ_t)/ (n₁cosθ_i + n₂cosθ_t)

The Attempt at a Solution

I was just going to plot r vs degrees but i only know the incident angles, 0 though 90. What i do about the other angle?
I'm currently trying to plot it in excel. I think he expects us to plot it in MATLAB but i have no experience with matlab.

 

[nmsurobert]

i think i solved it. i can just use snells law and figure out the angle.