To Extend a Curve
1. In the Model Tree, right-click the Style feature that contains the curve to extend, and choose 
Edit Definition. The Style tab opens.
Edit Definition. The Style tab opens.2. Click > 
Curve Edit. The Curve Edit tab opens.
Curve Edit. The Curve Edit tab opens.3. Under Curve, click the 
collector, and select a curve.
collector, and select a curve.4. Extend the curve by performing one of these actions:
◦ To extend a curve and keep the number of points on the curve the same, select an end point, and drag the curve to extend it.
◦ To extend a curve by adding points to it, hold down SHIFT and ALT simultaneously, click the endpoint of the curve, and click outside the curve. A point gets added to the curve.
◦ To extend a curve by adding a point along the tangent or curvature extension of the curve, select the Point tab, and in the Extend box, select Tangent or Curvature from the list. Hold down SHIFT and ALT simultaneously and drag the new endpoint of the curve to the desired location along the tangent or curvature line.
5. Click 
OK.
OK.