In this clip the teacher leads a discussion about why arccos and arcsin gave different results.
Worksheet 6, Clip 3, Discussion of Question 3, Part I, 1:23
The teacher begins by having them recall what the inputs are for the trig functions and using that and their prior knowledge about inverse functions to help the students formalize what the inputs for the inverse trig functions are.
Notice that again the teacher is pushing the students to work in terms of radians, or percentage of the radius. This repetition is necessary to ensure the students are using the same language.