Chapter 10 - Parametric Equations and Polar Coordinates - 10.6 Conic Sections in Polar Coordinates - 10.6 Exercise - Page 728: 2

$r= \frac{3}{1 - cos(θ)}$

$r= \frac{ed}{1 + e cos(θ)}$ e = 1 since it is an parabola, directrix is at x=-3. Origin is at (0,0) so d= 3, but it will be - cos(θ) since the directrix is negative $r= \frac{(1) (3)}{1 - (1) cos(θ)}$ $r= \frac{3}{1 - cos(θ)}$