# 5.2 Built-in Module `cmath`

This module is always available. It provides access to mathematical functions for complex numbers. The functions are:

`acos` (x)
  Return the arc cosine of x.

`acosh` (x)
  Return the hyperbolic arc cosine of x.

`asin` (x)
  Return the arc sine of x.

`asinh` (x)
  Return the hyperbolic arc sine of x.

`atan` (x)
  Return the arc tangent of x.

`atanh` (x)
  Return the hyperbolic arc tangent of x.

`cos` (x)
  Return the cosine of x.

`cosh` (x)
  Return the hyperbolic cosine of x.

`exp` (x)
  Return the exponential value .

`log` (x)
  Return the natural logarithm of x.

`log10` (x)
  Return the base-10 logarithm of x.

`sin` (x)
  Return the sine of x.

`sinh` (x)
  Return the hyperbolic sine of x.

`sqrt` (x)
  Return the square root of x.

`tan` (x)
  Return the tangent of x.

`tanh` (x)
  Return the hyperbolic tangent of x.

The module also defines two mathematical constants:

`pi`
  The mathematical constant pi, as a real.

`e`
  The mathematical constant e, as a real.

Note that the selection of functions is similar, but not identical, to that in module `math`. The reason for having two modules is, that some users aren't interested in complex numbers, and perhaps don't even know what they are. They would rather have `math.sqrt(-1)` raise an exception than return a complex number. Also note that the functions defined in `cmath` always return a complex number, even if the answer can be expressed as a real number (in which case the complex number has an imaginary part of zero).