So the question is asking to define and compare radian measure to degree measure, and base on my further research and further understanding about the said topic, the answer would be the following:
#1 in calculating arc length, the angle MUST be in radians.
#2 in formulas such as that for area of a circle (A = pi*r^2), pi (a measure of central angle) is already in radians.
#3 in Calculus (which you may or may not study later on), angles are commonly expressed in radians and not in degrees.
