Page 37 - DIGITAL BOOK MUHAMMAD AZWARDI NASUTION
P. 37

Jumlah n suku pertama deret geometri




        S =        a +     ar +      ar +        ....+      ar   n−  2   +   ar   n− 1
                                          2
           n

        rS =                ar +     ar +         ar +        ....+      ar   n−  2  +   ar   n−  1  +   ar   n     −
                                                       3
                                          2
             n


        S −        rS =         a −     ar   n
                        n
           n

                         ) ( 1−
        S  n (1−      r =       a          r  n  )



                    a  ( 1−    r  n )
        S =

           n
                        1−     r


        untuk         r      1
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