I've heard, a few times in my life, that something like 90%+ of mathematics that currently exists cannot be solved. That's amazing to me.... Anyone have anything to share on this? One of my professors was explaining to me that a lot of the equations that we're being taught (e.g. spring forces, aero drag...) are approximations to non linear equations. Call me weird, but I love hearing about this stuff. It's pretty humbling. Anyone?