Question

the sum 3 + 5 + 7 + 9 + •••• n =_____

Answer 1

Ans.

The common difference (d) = 2
The first element (a) = 3.

So, the n-th term is
I = a + (n-1).d
= 3 + (n-1)×2
= 1 + 2n.

So the required sum is
= (n/2)(a + I)
= (n/2)( 3 + 1 + 2n)
= (n/2)(4 + 2n)
= n (n+2)

Answer 2

$\huge\bf\fbox\red{Answer:-}$

The common difference (d) = 2

The first element (a) = 3.

So, the n-th term is

I = a + (n-1).

d= 3 + (n-1)×2= 1 + 2n.

So the required sum is

= (n/2)(a + I)

= (n/2)( 3 + 1 + 2n)

= (n/2)(4 + 2n)

= n (n+2).