The first quadrant goes from 0 to pi/2
The second quadrant goes from pi/2 to pi
The thrid quadrant goes from pi to 3pi/2
And the fourth quadrant goes from 3pi/2 to 2pi
So to find what quadrant a radian less than 0 or more than 2 pi is, you need to divide that angle by 2pi and then find the remainder. So for example, let's say we have 19pi/3. Now let's divide that by 2pi
19pi/3 / (2pi) = 19pi/3 * 1/(2pi) = 19pi/6pi = 19/6
So the remainder is 1. Now we originally had 19pi/3. So now all we have to do is replace the 19 with a 1 to get 1pi/3 radians or simply pi/3 radians. pi/3 radians is in quadrant 1, so that means 19pi/3 is also in quadrant 1.
