Answers

2016-08-01T22:04:52+08:00
I think it's supposed to be -8
anyway, the summation is 10502~
0
2016-08-02T20:06:07+08:00
Formula Sn= N/2 [2(a1)+(n-1)]d     Finding d is -11+-14=3                       Our Nth term is 89 so ...
            Sn= 89/2 [2(-14)+(89-1)3
            Sn=89/2  (-28+88*3)
            Sn=89/2  (-28+264)
            Sn=89/2  (236/1)
            Sn=21004/2
            Sn=10502
0