def demo_Arcs_extend(sketch: adsk.fusion.Sketch):
# Define three points and create an arc along those points
startPoint = adsk.core.Point3D.create(0, 0, 0)
alongPoint = adsk.core.Point3D.create(5, 3, 0)
endPoint = adsk.core.Point3D.create(8, 0, 0)
arcs = sketch.sketchCurves.sketchArcs
arc = arcs.addByThreePoints(startPoint, alongPoint, endPoint)
# Create a line to extend the arc to.
lineStart = adsk.core.Point3D.create(-2, -3, 0)
lineEnd = adsk.core.Point3D.create(10, -3, 0)
lines = sketch.sketchCurves.sketchLines
line = lines.addByTwoPoints(lineStart, lineEnd)
# Extend the end point of the arc.
extendedCurve = arc.extend(endPoint)