if the 1st term of a series is 7 and the 13 th terms is 35 find the sum of 13 terms of the sequence
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a=7
a+12d=35
according to the question
a+12d=35
→7+12d=35
→12d=35-7
→12d=28
→d=28/12
→d=7/3
so,
sn=n/2[2a+(n-1)d]
→s13=13/2[2(7)+(13-1)7/3]
=13/2(14+84/3)
=13/2(14+28)
=13/2×42
=273
Therefore,sum of 13th term is 273 by above statement.
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