Question

find the sum of n term of A.P.whose r term is 2r+3

Answer 1

Answer:

n( 4 + n)

Step-by-step explanation:

ar = 2 r + 3

a1 = 2(1) + 3 =5

an = 2n + 3

sum of n terms  = n/2 (a1 + a2)

= n/2 ( 5 + 2n + 3)

= n/2 ( 8 + 2n)

n/2 × 2(4 + n )

⇒n( 4 + n)

hence sum of n terms is n( 4 + n)

Answer 2

Answer:

n(4+n)

Step-by-step explanation:

ar= 2 r + 3

a1 = 2(1) + 3 = 5

an = 2n + 3

sum of n term =n/2(a1+a2)

=n/2 (5+ 2n + 3)

=n/2 (8+2n)

n/2 × 2 ( 4+ n)

n( 4 +n)

hence sum of n term is n(4 + n)