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):
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.
