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Question

The sum of first n terms fo an AP is (5nn2) the nth term of the AP is
(a) (5-2n) (b) (6-2n) (c) (2n-5) (d) (2n-6)

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Solution

Given that sum of the first n terms of an AP is (5nn2)

Sn=(5nn2)

First term, a1=S1=5(1)(1)2=51=4

Sum of first two terms S2=5(2)(2)2=104=6.

Second term, a2=S2S1=64=2

d=a2a1=24=2

an=a+(n1)d

=4+(n1)(2)

=42n+2

=62n.

∴ nth term of an A.P = 6 - 2n.
option b is correct


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