Question

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

Answer 1

Answer:

an= 2n+1

Step-by-step explanation:

put n=1

a1 = 2 +1 =3

put n=2

a2= 4+1 =5

a2-a1 =5-3=3  { common difference}

now,

a2 = a+d

5=a+3

a=2

Sn =n/2 {2a +(n-1)d}

Sn= n/2( 4+ (n-1)3 )

Sn= n/2( 4+ 3n-3 )

Sn=n/2 (1+3n)