Limits of integration with polar coordinates.

Ok, I have the following problem find the area inside the cardioid

and outside the circle

I know you check for the limits of integration by finding where the two graphs intersect which is

However they show how the solution is done im a trying to re work it and they say you can just take the area of half the region and multiply it by two which gives the these limits of integration

How the hell that came up? I cant see where the right half the graph starts at -pi/2