/*         .c                       freeware                   [[Email Removed]]
*/

/* --------------------------------- INCLUDES ------------------------------- */
#include "xa_hfile.h"
#include    "f___4.h"
/* --------------------------------- MAIN ----------------------------------- */
int main(void)
{
double (*P_f)(double x);
double (*pDf)(double x);

double c = .5;
double t;
/*-------------------------------- PROGRAM ---------------------------------- */
 P_f =  f;
 pDf = Df;

 clrscrn();
 printf("  f : x-> %s\n\n", feq);
 printf(" Df : x-> %s\n\n\n",Dfeq);

 printf(" With c = %0.3f, the equation of the tangent is :\n\n",c);
 printf("       Df(c) (x-c) + f(c) = ");
 eq_Tan(  c,
       (*P_f),
       (*pDf)
       );
 printf("\n\n\n");

 printf(" Find PA, the length of the tangent from P to the x axis.\n\n");

 t = ((*P_f)(c));
 printf(" P(%6.3f, %6.3f)           P(           c, f(c))       \n", c, t);

 t = c- ( ((*P_f)(c)) / ((*pDf)(c)) );
 printf(" A(%6.3f, %6.3f)           A(c-f(c)/Df(c),    0)\n\n\n",t, 0.0);

 t = ((*P_f)(c)) * sqrt(1+(1/ pow(((*pDf)(c)) ,2)   ));
 printf(" PA = f(c) sqrt(1 + (1/Df(c)**2)) = %6.3f\n\n\n", t);
                       
                         /* plot [xmin:xmax] [ymin:ymax] */
 gplt_TanPx    (-4,      /* xmin  */
                 4,      /* xmax  */
                -4,      /* ymin  */
                 4,      /* ymax  */
                 c,
               feq,
            (*P_f),
           (*pDf));

 printf(" To see the graph, open the file \"f_Df.plt\" with Gnuplot.\n\n");
 printf(" Press return to continue\n");
 getchar();

 return 0;
}