Question

How to find the reference angle of -11pi/3 ? 

Answer 1

Just replace π by 180°

$\boxed{-\frac{11\pi}{3}=-\frac{11*180}{3}=-660^o=60^o}$

Answer 2

$- \frac{11 \pi }{3} \\ \\ =- \frac{11*180}{3} \\ \\ =- \frac{1980}{3}$

$=-660$ °

= 60 °