...The problem says:
A swimming pool is circular with a 40-ft diameter. The depth is constant along east-west lines and increases linearly from 2ft at the south end to 7ft at the north end. Find the volume of water in the pool.
I'm having trouble finding the equation of this plane. I would think two points are (0,20,7) and (0,-20,2).
However, I'm having trouble finding a third point. <---- (20, 0, 4.5)
I know that from three points I can find two vectors, then a normal vector, and then the equation of the plane.