Question

if the nth term of ap is (2n+1)find the sum of first n terms of the ap

Answer 1

$an = (2n + 1) \\ a1 = 2(1) + 1 = 2 + 1 \\ = 3 \\ a2 = 2(2) + 1 \\ = 4 + 1 \\ = 5 \\ sn = \frac{n}{2} (2a + (n - 1)d) \\ sn = \frac{n}{2} (2(3) +( n - 1)2 \\ = \frac{n}{2} (6 + 2n - 2) \\ sn = \frac{n}{2} (4 + 2n)$
hope this helps you quickly