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Question
If the sum of n terms of an A.P. is given by Sn = 3n + 2n2, then the common difference of the A.P. is ______.
Options
3
2
6
4
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Solution
If the sum of n terms of an A.P. is given by Sn = 3n + 2n2, then the common difference of the A.P. is 4.
Explanation:
Given that Sn = 3n + 2n2
S1 = 3(1) + 2(1)2 = 5
S2 = 3(2) + 2(4) = 14
S1 = a1 = 5
S2 – S1 = a2
= 14 – 5
= 9
∴ Common difference d = a2 – a1
= 9 – 5
= 4
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