Question

if the 9th term of an AP is (2n+1) find the sum of first n terms of the AP

Answer 1

here is your answer ⤵️

➡️ l = 2n+1

↪️ n=1

↪️ a=2(1)+1

↪️ a=3

➡️ A.P.=n/2(a+l)

➡️ A.P.=n/2(3+2n+1)

➡️ n/2(2n+4)

➡️ n(n+2)

Hence, sum of first n terms of an A.P. is n(n+2)

__hope it help ✌️