In an open
sketch, click Extend Entities 
on the Sketch toolbar, or click Tools,
Sketch Tools,
Extend.
You can add to the length of a sketch entity (line, centerline, or arc). Use Extend Entities to extend a sketch entity to meet another sketch entity.
To extend a sketch entity:
In an open
sketch, click Extend Entities on the Sketch toolbar, or click Tools,
Sketch Tools,
Extend.
The pointer
changes to 
.
Move the pointer over the sketch entity to extend.
The selected entity appears in red, and a preview appears in red in the direction to extend the entity.
If the preview extends in the wrong direction, move the pointer to the other half of the line or arc .
Click the sketch entity to accept the preview.
To extend a sketch entity beyond the closest
entity, click to place the first sketch extension, drag towards the next
sketch entity, then click place the second extension, etc.
