Plot3D[{Sqrt[8 - x^2 - y^2], Sqrt[x^2 + y^2]}, {x, -4, 4}, {y, -4, 4}]

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.