I'm not sure this is the right forum, I hope the moderator will move it if necessary.

(1) I have to sketch level sets , c=1, 0, -1, for the function

I know level sets are but how do i sketch this? :(

(2) Let be the inverse of stereographic projection from to the equatorial hiperplane . Show that for every vector exists such that

.

I don't even know how to start..

Thank you for your time and help!