Arithmetic Sequence

Sequence: -13 -10 -7 – ….. +62      Determine the sum of the arithmetic sequence

62 = -13 + (n-1) (3)

+13    +13       —–> 75 = (n-1) (3) —–> \frac{75}{3} = (n-1) (\frac{3}{3}) ——-> 25=n-1  =    n = 26

/prt 2   S_{26} =  \frac{26}{2} (-13+62)   —–>   S_{26} = 13 (49)    —->    S_{26} = 637