terminacion de la tarea 2

7.- a1= 2 an= 215 n= 164

sn=(2+215)164                      sn=(217)164                       sn=35588
    ___________                        ___________                      ______=17794
             2                                          2                                         2

8.- a1= 21 an= 276 n= 321
sn=(21+276)              sn=(297)321          sn=95337
 __________                  ________          ________=476685
         2                                  2                           2
           
9.- a1= -78 d= -49
sn=-78+49   (n-1)              (n-1)=127
sn=127       (n-1)                  n=127+1=128

10.- a1= 345 d= -169
sn=345+169    (n-1)                            (n-1)=514
sn=514      (n-1)                                 n=514+1=515