Chapter 10 - Parametric and Polar Curves - 10.2 Polar Coordinates - 10.2 Exercises - Page 729: 27

$$x = - 4$$ $${\text{The graph or the curve is the vertical line }}x = - 4$$

$$\eqalign{ & r\cos \theta = - 4 \cr & {\text{Where }}r\cos \theta = x.{\text{ So}}{\text{,}} \cr & x = - 4 \cr & {\text{The graph or the curve is the vertical line }}x = - 4 \cr} $$