Trigonometric functions

### 5.21.1 Trigonometric functions

- sin is the sine function,
- cos is the cosine function,
- tan is the tangent function (tan(x)= sin(x)/cos(x)),
- cot is the cotangent function (cot(x)= cos(x)/sin(x)),
- sec is the secant function (sec(x)= 1/cos(x)),
- csc is the cosecant function (csc(x) = 1/sin(x)),
- asin or arcsin, acos or arccos, atan or arctan, acot, asec, acsc are the inverse trigonometric functions. The latter are defined by:
  1. asec(x) = acos(1/x),
  2. acsc(x) = asin(1/x),
  3. acot(x) = atan(1/x).