To trim several entities using the fence selection method

Do one of the following:

Choose Modify > Trim.
On the Modify toolbar, click the Trim tool ().
Type trim and then press Enter.

Select one or more cutting edges, and then press Enter.
In the prompt box, choose Fence.
Specify the first point of the fence.
Specify the second point of the fence.
Specify the next fence point, or press Enter to complete the command.

Select the boundary edge (A), and then specify the first point (B) and second point (C) of the fence.

Result.

How do I...

Trim an entity to an implied boundary