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.

You can use the Quick Trim feature in this instance to trim or extend entities with a simple cursor selection: click Edit>Settings>Quick Trim to enable it.