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`cosh', `coshf'--hyperbolic cosine

     #include <math.h>
     double cosh(double X);
     float coshf(float X)
`cosh' computes the hyperbolic cosine of the argument X.  `cosh(X)' is
defined as
      (exp(x) + exp(-x))/2
   Angles are specified in radians.  `coshf' is identical, save that it
takes and returns `float'.
The computed value is returned.  When the correct value would create an
overflow,  `cosh' returns the value `HUGE_VAL' with the appropriate
sign, and the global value `errno' is set to `ERANGE'.
   You can modify error handling for these functions using the function
`cosh' is ANSI.  `coshf' is an extension.