Trigonometric function is one of the basic elementary functions, which takes the angle (the most commonly used radian system in mathematics, the same below) as the independent variable, and the angle corresponds to the coordinates where the terminal edge of any angle intersects with the unit circle or its ratio as the dependent variable. It can also be equivalently defined as the lengths of various line segments related to the unit circle.
Trigonometric function knowledge points:
Sine: The opposite side of angle A is the hypotenuse.
Cosine (cos): The adjacent side of angle α is higher than the hypotenuse.
Tangent (tan): The opposite side of angle A is greater than the adjacent side.
Cotangent: The adjacent side of angle α is greater than the opposite side.
Secant: The hypotenuse of Angle A is higher than the adjacent side.
Cotangent: The hypotenuse of angle α is higher than the edge.