Asked by Anonymous

Find the sum of 35 terms of an arithmetic series of which the first term is "a" and the fifteenth term is "9a."

Answers

Answered by Reiny
1st term --- a
15th term = a + 14d = 9a
14d = 8a
d = 4a/7

sum(35) = (35/2)(2a + 34d)
= (35/2)(2a + 34(4a/7)
= (35/2)(150a/7)
= 375a
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