|   | 1 |  initial version  | 
nevermind.
Q=arrow3d((0,1,-1), (1,2,0), color="green") P=arrow3d((0,1,0), (2,3,1), color="red") show(P+Q, figsize=5)
works. from: http://sagemath.wikispaces.com/line3d
 Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.
 
                
                Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.