1. What does the equation y = 9 represent in R3? a. a point b. a line c. a plane d. a circle 2. What does z = 2 represent? a. a point b. a line c. a plane d. a circle 3. What does the pair of equations y = 9, z = 2 represent? In other words, describe the set of points (x, y, z) such that y = 9 and z = 2. a. a point b. a line c. a plane d. a circle