Trim and Extend
From AutoCAD 2006 a new feature in AutoCAD has appeared. In the TRIM command you can switch to extend by holding down SHIFT, you select the objects first and then press down shift while you click on the end of a line you wanna extend. You can do the same with Extend command, switch to Trim. But there are also more functionality in these 2 commands. Especially the options Fence and Edge are worth mentioning. With fence at hand you can easily trim or extend multiple lines by making a long cutting line in 2 clicks! The other option I should mention is Edge. With Edge you can extend to a invisible boundary. There should bea line to make an invisible extension with. Select the option Edge in the Extend command. When AutoCAD prompt; "Enter an implied edge extension mode [Extend/No extend] :" Type E enter. Next picka line to make an extension with (boundary). Job done!