ContourPlot3d[3x^2 + 3y^2 + 3z^2 + 8xz - 8xy - 8zy == 0, {x,-100,100},{y,-100,100},{z,-100,100}]

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.