Question

IF THE nth TERM OF AN A.P IS (2n+1), FIND THE SUM OF FIRST n TERMS OF AN A.P.

Answer 1

Sum of n terms in an AP is given by

s= n/2(2a+(n-1)d)

where
s = sum of progression
n = number of terms
a = value of first term
d = difference between 2 terms

now, the first term in your question is 3 (2 x 1 + 1)
so, a = 3
second term is 5

third is 7, like that

so d = 2

Therefore, the sum of first n terms of the AP will be

n/2 [2 x 3 + (n-1) 2]

simplifying, we get the sum as

n [3+n-1]

n (n+2)

Hope it helps
All the best.