Question

4. if the nth term of an a.p. is (2n + 1), find the sum of first n terms of the a.p.

Answer 1

Answer:

n (n+2)

Step-by-step explanation:

The 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

The first term inthe question is 3 (2 x 1 + 1)

so, a = 3  and second term is 5  and third is 7, thus the series can be 3,5,7,9

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)