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2015-03-20T10:05:49+05:30
An=2-3n
n=1,an1=2-3x1=-1
n=2,an2=2-3x2=2-6=-4
common difference=an2-an1=-4-(-1)=-4+1=-3
Sn=n/2{2a+(n-1)d}
given n=30,first term -1,common difference=-3
s30=30/2{2(-1)+(30-1)-3}
S30=15{-2-87}
S30=-1335



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2015-03-20T10:11:15+05:30
An=2-3n
so
a1=2-3*1
   =-1
a30=2-3*30
     =-88
so
 sum=n/2(a1+a30)
       =30/2(-1+-88)
       =15(-89)
       =-1335
2 5 2