Chapter 10 - Conics, Parametric Equations, and Polar Coordinates - Review Exercises - Page 743: 69

$$r = 9\csc \theta $$

$$\eqalign{ & y = 9 \cr & {\text{Convert to polar form, using }}y = r\sin \theta \cr & r\sin \theta = 9 \cr & \frac{{r\sin \theta }}{{\sin \theta }} = \frac{9}{{\sin \theta }} \cr & r = 9\csc \theta \cr & {\text{The graph represents a horizontal line at }}y = 9 \cr & {\text{Graph}} \cr} $$