Question

If the nth term of an AP is(2n+1), find the sum of first n terms of the AP.​

Answer 1

We have,

an=(2n+1)⟹a1=2×1+1=3

So, the given sequence is an A.P. with first term a=a1=3 and last term l=an=2n+1.

Therefore, the sum of n terms is given by

Sn=2n(a+l)=2n{3+(2n+1)}=2n(2n+4)=n(n+2)

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