SOLUTION: The last three terms of an arithmetic sequence with 18 terms is as follows: 67,72,77. How do you find the first term and the sum of the series
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Question 1002107: The last three terms of an arithmetic sequence with 18 terms is as follows: 67,72,77. How do you find the first term and the sum of the series Answer by ikleyn(52788) (Show Source):
This arithmetic progression has the common difference d = 77 - 72 = 5 and
= 77, according to the condition.
= + d*(18-1) = + 5*17 = + 85.
Thus you have an equation to find :
+ 85 = 77.
It gives you = 77 - 85 = -8.
