Use Trim/A,to,L or Trim/A,to,C to trim an arc to a line or circle boundary. The Start/End selector specifies which endpoint to trim.
Use Trim/A,to,L (trim arc to line) or Trim/A,to,C (trim arc to circle). The Start/End selector specifies which endpoint of the arc to trim. The arc must intersect the boundary within its sweep angles.