I can’t find arccos or any of the other inverse trig functions in the material editor… Is there a way I can maybe implement it or find it elsewhere?
You can do it using the custom node. Look into the asin(x), acos(x) and atan2(x) functions. Those should return the inverse sine, cosine and tangent in radians.
I suggest you bookmark this page as sooner or later you may need many of these:
That said the inverse functions can be expensive. For what do you need them? There is often a cheaper way to come up with the same information using different math that runs faster on the GPU.