Worksheet 5, Clip 3, Discussion of Question 5, 1:37
The students suggest using sine and cosine functions. Notice that the teacher probes them as to why that will work. This will keep it from being just a procedure and help the students form a deeper understanding. To reinforce the relationship between the inputs (arc length) and the output (fraction of the radius) the teacher makes sure to have them report the units for their answers.
Also the teacher points out that since their radius is 1, what they have for an angle measure is also their arclength. This continual reinforcement will be helpful when students begin working with circles of different radii.