4 angles whose sine equals 1/2

sin^-1(0.5)  =  30^o plus every integer number multiple of 360^o:  30^o, 390^o, 750^o, etc.

Also:  sin^-1(0.5)  =  150^o plus every integer number multiple of 360^o:   150^o, 510^o, 870^o, etc.