Так как sin a = 4/5, то cos a = √1−sin2a1 - sin²a1−sin2a = √1−16/251 - 16/251−16/25 = √9/259/259/25 = 3/5.
Тангенс a = sin a / cos a = 4/54/54/5 / 3/53/53/5 = 4/3.
Котангенс a = 1 / tan a = 1 / 4/34/34/3 = 3/4.
Итак, cos a = 3/5, tg a = 4/3, ctg a = 3/4.
Так как sin a = 4/5, то cos a = √1−sin2a1 - sin²a1−sin2a = √1−16/251 - 16/251−16/25 = √9/259/259/25 = 3/5.
Тангенс a = sin a / cos a = 4/54/54/5 / 3/53/53/5 = 4/3.
Котангенс a = 1 / tan a = 1 / 4/34/34/3 = 3/4.
Итак, cos a = 3/5, tg a = 4/3, ctg a = 3/4.