Extend Entities
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:
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In an open sketch, click Extend Entities 
on the Sketch toolbar, or click Tools, Sketch Tools, Extend.
The pointer changes to 
.
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Move the pointer over the sketch entity to extend.
A preview appears in the direction to extend the entity.
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If the preview extends in the wrong direction, move the pointer to the other half of the line or arc.
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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.
