Question

Find the 9th partial sum, s9, for the sequence 1, -1, 1, -1,....

Answer 1

The ninth partial sum:

We would determine the sequence to the ninth term:

Sn =  1, -1, 1, -1, 1, -1, 1,-1, 1,...

S₉ =   1 + (-1)  +  1 +  (-1) + 1+ (-1)+ 1+ (-1) +1  = 1.

 S₉ = 1