Use the Trim and Extend tools to trim or extend one or more elements to a boundary.
This video demonstrates the following:
There are 3 types of trim and extend tools you can use, depending on the situation. The relative position of the elements and where you click determines whether an element is trimmed or extended.
Trim/extend to corner is the most common tool. Use this to join elements at a projected intersection point. Each element will be trimmed or extended as needed to create the corner condition. Select the trim/extend to corner tool, and then select the elements to join. When selecting the elements, you select the sides of the elements you wish to keep. For example, when these elements are selected, a corner can be produced to either side depending on which side of the horizontal element is selected.
Trim/extend a single element allows you to alter one element. Select the trimming/extending edge is first, and then select the element to be trimmed or extended. Again, the portion of the trimmed/extended element you want to keep is selected. When you use the single element trim/extend tool, the trimming edge must be re-selected between each trim/extend action.
Trim/extend multiple elements allows you to select the trimming edge once and then select multiple items to trim or extend to the edge. When you use the trim/extend multiple tool, use a window selection to choose multiple elements in one action.
Use the trim and extend tools to alter the geometry of elements after they have been placed in your model.