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

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)

thats all

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