[tex]\bf \cfrac{19}{6}\implies 3+\cfrac{1}{6}
\\ \quad \\\\
\cfrac{-19\pi }{6}\implies -\left(3\pi +\cfrac{1\pi }{6} \right)\impliedby clockwise
\\ \quad \\\\
or\implies -\left(2\pi +\pi +\cfrac{\pi }{6} \right)[/tex]
go that much "clockwise", you'll end up at the 2nd quadrant,
the reference angle, is its reflective angle on the 1st quadrant
