Describe the set of points whose distance from the y-axis equals the distance from the xz-plane.
- a cone opening along the x-axis.
- a cone opening along the y-axis.
- a cone opening along the z-axis.
- a cylinder opening along the x-axis.
- a cylinder opening along the y-axis.
- a cylinder opening along the z-axis.
Find an equation for the set of points.