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

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): You can put this solution on YOUR website!
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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.

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