The 2D object (such as circle, intersecting lines, arc) selected with the extend command is extended to the specified reference boundary. A 2-dimensional object is selected as the reference boundary.
Location of the Extend Command
You can access the Extend command under the Modify title of the ribbon menu Drawings tab .
Click the Extend icon in the ribbon menu .
Select the line that will be your reference border and click the right mouse button. It will be extended up to this line.
Determine the side of your other line to be extended.
Your line will be extended.
Determining the reference limit
Determining the side to be extended