To make it easier to follow the path of trend lines, you can extend the start and end points of trend lines you have created. You can also hide the extensions of trend lines.

NOTE: To select a Trend Line in the Chart window, you must display the Chart toolbar. To display the Chart toolbar, right-click the Chart window and select Show Toolbar from the Chart window pop-up menu. Click here for more information.
Perform the following to extend or hide the extensions of a trend line:
From the Chart
toolbar, click 
NOTE: If you do not see this button, you need to display
the Chart toolbar.
Perform one of the following to select one or more trend lines:
To select a single trend line, click a trend line so that it is selected.
To select multiple
trend lines, hold down the CTRL key and then click each trend line you
want to select.
Release the CTRL key.
TIP: You can also select multiple trend lines by clicking and
holding the mouse button while drawing a selection square over all of
the lines you want to select.
Right-click the mouse directly
over a trend line to display the Chart
pop-up menu.

NOTE: If the Drawing
menu option is not available, make sure to right-click the mouse directly
over a trend line.
Perform one of the following from the Chart pop-up menu:
To extend the start of the select trend line(s), select Drawing>Extend line start
To extend the end of the trend line(s), select Drawing>Extend line end
To remove both start and end trend line extensions, select Drawing>Do not extend line