The Trim Both function can be used to either trim or extend two intersecting entities to their intersection, or potential intersection, with each other.

Using the Function:

1. Select Both from the Curve>Modify>Trim Ribbon area.

2. Select the first entity to trim or extend, on the side you want to keep.

3. Select a second intersecting, or potentially intersecting, entity. The entity is trimmed or extended to the intersection. The side you select to keep remains.