Answers

2016-06-24T21:54:57+08:00
Sn=n/2[2a1+(n-1)d]
S6=6/2[2(81)+(6-1)-17]
S6=3[162+-85]
S6=3[77]
S6=231

Sn=number of terms to add
n=no. of terms
d=common difference
0