I assume that you are creating 2 different sketches which are containing lines
lets say , there are 2 sketches , and you want to join them , go to the generative shape design workbench and then choose insert + operations+ join choose the sketches from the tree ...then press ok.
and then if you make any changes just go to your sketch. apply the changes. it will update automatically .
Type "C:join" in the white box in the lower right hand corner of your screen. Once the function is activated, look to see which icon lights up - or look for "join" in your help documents.
Trim is used to extend a line, which is preferable to joining, assuming that you're not joining into a polyline. (for clarification of what I meant earlier)
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