vectors

[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?

[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

[Whatupdoc]

thanks alot, i get it now