Rumus Trigonometri Sudut Berelasi

Kuadran I

sin (90 - a) = cos a

cos (90 - a) = sin a

tan (90 - a) = ctg a

ctg (90 - a) = tan a 

Kuadran II

sin (180 - a) = sin a

cos (180 - a) = - cos a

tan (180 - a) = - tan a

ctg (180 - a) = - ctg a

sin (90 + a) = cos a

cos (90 + a) = - sin a

tan (90 + a) = - ctg a

ctg (90 + a) = - tan a

Kuadran III

sin (180 + a) = - sin a

cos (180 + a) = - cos a

tan (180 + a) = tan a

ctg (180 + a) = ctg a

sin (270 - a) = - cos a

cos (270 - a) = -sin a

tan (270 - a) = ctg a

ctg (270 - a) = tan a

Kuadran IV

sin (360 - a) = - sin a

cos (360 - a) = cos a

tan (360 - a) = - tan a

ctg (360 - a) = - ctg a

sin (270 + a) = cos a

cos (270 + a) = - sin a

tan (270 + a) = - ctg a

ctg (270 + a) = - tan a

Sudut Negatif 

sin (- a) = - sin a

cos (- a) = cos a

tan (- a) = - tan a

ctg (- a) = - ctg a

Pengulangan Sudut

sin (k . 360 + a) = sin a

cos (k . 360 + a) = cos a

tan (k . 360 + a) = tan a

ctg (k . 360 + a) = ctg a