Question

if the n th term of an AP 2n+1 find the sum of first n terms of an AP​

Answer 1

Answer:

Step-by-step explanation:

Given:

$A_n=2n+1\\\\A_1=a=2(1)+1=3\\\\A_2=2(2)+1=4+1=5\\\\d=A_2-A_1=5-3=2\\\\Thus \ sum \ of \ n \ terms \\\\S_n= \frac n2 [ 2a+(n-1)d]\\\\=\frac n2 [2\times3 +(n-1)\times2]\\\\=\frac n2 (6+2n-2)\\\\=\frac n2(2n+4)\\\\\bf { S_n=n(n+2)}$