Arduino trig and exponential functions use the avr-libc library. The library includes a great number of useful mathematical functions for manipulating floating point numbers.

The Atmega8 chip, which is now dated, but still supported, does not have enough memory to be able to use the math.h library so you will probably need to update to an Atmega168 if you wish to use any of these functions.

The full docs for math.h may be found here

List of more common functions with descriptions

This is just a partial list - check the docs for more obscure functions

double  cos (double __x)   // returns cosine of x
double 	fabs (double __x)  // absolute value of a float
double 	fmod (double __x, double __y) // floating point modulo
double 	modf (double __value, double *__iptr) // breaks the argument value into
                                              // integral and fractional parts
double 	sin (double __x)   // returns sine of x
double 	sqrt (double __x)  // returns square root of x
double 	tan (double __x)   // returns tangent of x
double 	exp (double __x)   // function returns the exponential value of x.
double 	atan (double __x)  // arc tangent of x
double 	atan2 (double __y, double __x) // arc tangent of y/x
double 	log (double __x)   // natural logarithm of x
double 	log10 (double __x) // logarithm of x to base 10.
double 	pow (double __x, double __y) // x to power of y
double  square (double __x) // square of x

See also