SOLUTION: the sum of the first 20 terms of an AP series is identical to the sum of the first 22 terms. If the common difference is -2 find the first term?

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Question 1128870: the sum of the first 20 terms of an AP series is identical to the sum of the first 22 terms. If the common difference is -2 find the first term?
Answer by ikleyn(52788)   (Show Source): You can put this solution on YOUR website!
.
The condition immediately implies that the sum 

     +  = 0.


Thus   = -.


From the other side,   =  = .


It implies   = -2;  hence,   = -1.



From the other side,   =  =  = .


Hence,   =  = -1 + 42 = 41.


Answer.   = 41.

Solved.

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