# Find the equation of the sphere

1. Aug 27, 2005

### Whatupdoc

Find the equation of the sphere centered at (-6,-7,-1) with radius 9.

well i got $$(x+6)^2 + (y+7)^2 + (z+1)^2-9^2$$ which is correct.

now for the next question:

Give an equation which describes the intersection of this sphere with the plane $$z=0$$.

i dont understand how to do the second question at all, can someone help?

2. Aug 27, 2005

### iNCREDiBLE

What you got must've been:
$$(x+6)^2 + (y+7)^2 + (z+1)^2-9^2 = 0$$.

The equation that describes the intersection with the plane z = 0 must be:
$$(x+6)^2 + (y+7)^2 + (0+1)^2-9^2 = (x+6)^2 + (y+7)^2 - 80 = 0$$

3. Aug 27, 2005

### Whatupdoc

thanks alot, i get it now