So, I was in Audacity messing around with phase inversion when I found i could take 2 verses of the same song (with repeated instrumentals, such as rap music) and make a combined acapella (vocals only) of those 2 verses using phase inversion. However, I want to know if it’d be somehow possible to get the exact OPPOSITE, the combined instrumental only. If anybody could provide an answer I’d be cool with that. Thanks! 
Phase Inversion tricks come with an awkward “feature.” They appear that you should be able to work the trick backwards…and you generally can’t.
The only two pre-packaged Audacity tricks are Effect > Vocal Remover and Effect > Vocal Reduction and Isolation.
http://manual.audacityteam.org/man/vocal_remover.html
http://manual.audacityteam.org/man/vocal_reduction_and_isolation.html
They work on a stereo track and need the vocal to be in the exact middle of the stereo field and the rest of the music not to be. Doesn’t work at all on mono (one sound wave) tracks.
Koz