The square root of -1. How did they figure out that that could be useful? The things that get done when there is no TV to watch..
Or those parabola things. Who the **** cares which way the damn arrows go? It's a ******* answer....why do you need to graph it to prove it's right? And geometry proofs. Kiss my ***. I can look at the shape and tell it's a ******* square. I don't need to PROVE it.