00:01
In this question, i want to describe in words the region of three -dimensional space that's represented by the inequality.
00:09
I have x squared plus y squared plus z squared is greater than 2z.
00:14
So to see what's happening here, i'm going to start by setting this to zero.
00:19
I'm going to subtract 2z to the left -hand side.
00:25
So i'm getting x squared plus y squared plus z squared minus 2z is greater than zero.
00:36
Now i have this quadratic in z and i want to complete the square on that quadratic in z.
00:46
So what do i do? i take half of my b, half of negative 2, which is negative 1, and i square.
00:54
That gives you positive 1.
00:56
And i'm going to add that to each side...