The sum of n terms of an arithmetic series is given as:
Sn = 5n^2 - 11n
Sn-1 = 5(n - 1)^2 - 11(n - 1)
=> 5(n^2 + 1 - 2n) - 11n + 11
=> 5n^2 + 5 - 10n - 11n + 11
=> 5n^2 - 21n + 16
The term tn = Sn - Sn-1
=> 5n^2 - 11n - 5n^2 + 21n - 16
=> 10n - 16
The common difference = tn - tn-1
=> 10n - 16 - (10(n - 1) - 16)
=> 10n - 16 - 10n + 10 + 16
=> 10
The common difference of the series is 10
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