Mathc initiation/a175

Sommaire

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	s_an.h

/* --------------------------------- */
/* save as s_an.h                    */
/* --------------------------------- */
double S_an(
int n,
double a_1,
double r)
{ 	
 return(a_1*(1-pow(r,n))/(1-r));
}
char  S_aneq[] = "[a_1 (1-r**(n))/(1-r)";
/* --------------------------------- */
/* --------------------------------- */
/*  Compute the partial sum of the sequence a_n = a1 r**n 


   S_n = 1  + r + r**2 + ... + r**n-1 
  rS_n =      r + r**2 + ... + r**n-1 + r**n   
           -------------------------------------------------
   S_n - rS_n = (1-r**n) 
     
                                                                              
    S_n (1-r) = (1-r**n) 
 
                                   ___n
                (1-r**n)           \                  (1-r**n)   
          S_n = --------           |   a_1 r**n = a_1 -------- 
                 (1-r)             /__                  (1-r) 
                                      n=1 

*/    
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