det {{ 1, -1, 0, 0 },{ -1, 2, -1, 0 },{ 0, -1, 1, 0 },{ 0, 0, 0, 0}}

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.