Sine function sin (a) = a/c.

Cosine function cos (a) = b/c.

Tangent function tan (a) = a/b.

Cotangent function cot (a) = b/a.

Where a is the opposite side, b is the edge and c is the hypotenuse.

Some special trigonometric function values.

sin0=0

cos0= 1

tan0=0

trigonometric function

Trigonometric function is a transcendental function in elementary functions in mathematics. Their essence is the mapping between any set of angles and a set of ratio variables.

The usual trigonometric function is defined in a plane rectangular coordinate system. Its definition field is the whole real number field. The other is defined in a right triangle, but it is incomplete. Modern mathematics describes them as the limit of infinite sequence and the solution of differential equation, and extends their definitions to complex system.