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Nov 2014 p12 q8
846
The sum, \(S_n\), of the first \(n\) terms of an arithmetic progression is given by \(S_n = 32n - n^2\). Find the first term and the common difference.
Solution
Given the sum of the first \(n\) terms of an arithmetic progression: \(S_n = 32n - n^2\).
To find the first term \(a\), set \(n = 1\):
\(S_1 = 32(1) - 1^2 = 32 - 1 = 31\).
Thus, the first term \(a = 31\).
To find the common difference \(d\), set \(n = 2\):
\(S_2 = 32(2) - 2^2 = 64 - 4 = 60\).
The second term is given by \(S_2 - S_1 = 60 - 31 = 29\).
The common difference \(d = 29 - 31 = -2\).
Therefore, the first term is 31 and the common difference is -2.