7 %7B1%2C 0%2C -2%2C 1%7D - 4 %7B2%2C -1%2C 1%2C -1%7D

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.