5
4
3
2
Correct answer is D
Sn=n2(2a+(n−1)d
n2(2a+(n−1)d=n2+2n
n(2a+(n−1)d=2n2+4n
2an+n2d−nd=2n2+4n
Comparing the equations, d = 2 (coefficient of n2).
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