Focused mostly on arclength.

The equation used is that for circumference. And then you figure out the fraction of the circle. Which could be any amount, sometimes it was 1/2 for a semicircle.

You can convert between radians and degrees using a conversion factor, just like you would for cm to inches, etc.

Reviewed some common angles in radians, which are often fractions of pi.

2r is the diameter. So if the diameter is given, you can substitute it for 2r.