Find the sum of 35 terms of an arithmetic series of which the first term is a and the fifteenth term is 9a.
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an = a+(n-1)d
a15=a+(15-1)d
9a= a+14d
8a= 14d
a= 14d/8
a= 1.75d
sn=n/2× 2a+(n-1)d
s35=35/2×2×1.75d+34d
s35= 17.5×71.5d
s35= 1251.25d
hence the sum of 35 term = 1251.25d
a15=a+(15-1)d
9a= a+14d
8a= 14d
a= 14d/8
a= 1.75d
sn=n/2× 2a+(n-1)d
s35=35/2×2×1.75d+34d
s35= 17.5×71.5d
s35= 1251.25d
hence the sum of 35 term = 1251.25d
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