Tài liệu Drawing in Two Dimensions

To trim an object, choose Trim from the Modify toolbar. You cannot select
objects before starting the TRIM command. AutoCAD displays the Current
settings: Projection=UCS, Edge=None Select cutting edges . Select
objects: prompt. AutoCAD lets you know the values of the two system variables
that affect trimming. The Projection setting is used only for 3D models. The Edge
setting is used for implied intersections. When Edge is set to Extend, AutoCAD
trims to the implied intersection of the cutting edge and the object to be trimmed.
At this prompt, pick the object(s) that you want to use as a cutting edge. Press
Enter to end object selection.
If the object you want to use for the cutting edge is already selected before
you start the TRIM command, AutoCAD deselects it. At the Select cutting
edges . prompt, you can type p ↵ to reselect that object.
You can trim to an actual or an implied intersection (an intersection that would
exist if objects were extended):
✦ If you want to trim to an actual intersection, at the Select object to trim
or shift-select to extend or [Project/Edge/Undo]: prompt, select
objects to trim. Be sure to pick each object between the cutting edge and the
end you want to trim off. Press Enter to end object selection. AutoCAD trims
the object(s).
✦ If you want to trim to an implied intersection, at the Select object to
trim or shift-select to extend or [Project/Edge/Undo]: prompt,
type e ↵. AutoCAD responds with the Enter an implied edge extension
mode [Extend/No extend] <No extend>: prompt. Type e ↵. Then select
the objects that you want to trim at the Select object to trim or
shift-select to extend or [Project/Edge/Undo]: prompt. Be sure
to pick each object at or near the end that you want to trim. Press Enter to
end object selection. AutoCAD trims the object(s).