Answers

2016-07-08T12:17:07+08:00
Tn= t1+(n-1)d
tn= 10+(15-1) (-3)
tn=10+(14)(-3)
tn= 10+(-42)
tn= -32

sn=n/2(t1+tn)
sn=15/2 (10+-32)
sn=15/2(-22)
sn= 165
the sum is 165
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