( sin (- (PI / 6)) = - (1 / 2) & cos (- (PI / 6)) = (sqrt 3) / 2 & tan (- (PI / 6)) = - ((sqrt 3) / 3) & sin (- (PI / 3)) = - ((sqrt 3) / 2) & cos (- (PI / 3)) = 1 / 2 & tan (- (PI / 3)) = - (sqrt 3) ) by SIN_COS:31, SIN_COS4:1, Thm8, Thm9, Thm11, Thm12, Thm10, Thm13;