##240^o## has a reference angle of ##60^o## as indicated in the image below. A ##60^o## angle is a basic angle from one of the common triangles:

From their definitions:

##sin(240^o) = -sqrt(3)/2##

##cos(240^o) = -1/2##

##tan(240^o) = sqrt(3)##

##csc(240^o) = – 2/sqrt(3)##

##sec(240^o) = -2##

##cot(240^o) = 1/sqrt(3)##