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`tan', `tanf'--tangent

     #include <math.h>
     double tan(double X);
     float tanf(float X);
`tan' computes the tangent of the argument X.  Angles are specified in
   `tanf' is identical, save that it takes and returns `float' values.
The tangent of X is returned.
`tan' is ANSI. `tanf' is an extension.