I agree with likesforests, I have often thought this would be useful to integrate a computer engine so that we can check lines. One issue I see is that because it is an online service, there might be technical difficulties. I don't know how hard it is to get a strong engine to run on the client machine (certainly we can't all be running an engine on the chess.com server). Some of the positions are pretty difficult and it would take a strong computer to solve them accurately.
I too am often copying the position over to Fritz by hand.
The tactics trainer should have an option to export a position (as a FEN string) and/or the analysis window should have a strong chess engine.
For example, suppose I try line #1 and it says line #2 is the winning line. I need to a way to check why line #1 was wrong so I can see what I missed (or perhaps the tactics trainer missed something... it happens!). Currently I have to hand-copy the position into another program, which is a painful and error-prone process.