Answer:
z ≤ √(81 -x² -y²)
Step-by-step explanation:
If the sphere is described in 3-D coordinates as ...
x² +y² +z² = r²
Then the upper surface is ...
z = √(r² -x² -y²)
With r=9, the solid volume below that surface and above the x-y plane is ...
z ≤ √(81 -x² -y²)
