Finding points of intersection (polar graphs)

Hey guys. I'm having trouble with the rationale used in my text regarding finding points of intersection given two polar graphs. I understand that to find the points I must set the equations equal, but then, this sometimes doesn't reveal all points of intersection. If someone would be so kind as to explain

1. why doesn't solving the system yield all points of intersection;

2. What is the best way to find these points?

I've provided an example problem so that you guys can illustrate this.

Find all points of intersectionof the graphs of the equations

$\displaystyle r=1+\cos{\theta}$ and $\displaystyle r=1-\cos{\theta}$ .

Thanks.