standard_description: Derive using similarity the fact that the length of the arc intercepted by an angle is proportional to the radius, and define the radian measure of the angle as the constant of proportionality; derive the formula for the area of a sector.
problem_activity: A rotation of 180° about the origin and reflections about two axis are equivalent transformations.
Describe two other sets of equivalent transformations. Provide a diagram to support your reasoning.


aligns: no