Creo Simulate > References > Sketcher > Manipulating Sketcher Geometry > To Trim and Extend Entities
  
To Trim and Extend Entities
1. Bring the pointer over the entity that you want to trim. The entity is highlighted.
2. Holding down the CONTROL key, drag the endpoint of the entity that you want to trim. The entity is trimmed or extended in the direction in which you drag it. At every intersection, the constraint that it created is displayed.