Question

Find the sum of first n natural numbers.

Answer 1

A.P. formed is 1, 2, 3, 4, ...., n.
Here,
a = 1
d = 1
l = n
So sum of n terms $=S_n=\frac{n}{2}[2a+(n-1\left)d\right]$
$=\frac{n}{2}[2+(n-1\left)1\right]$
$=\frac{n(n+1)}{2}$ is the sum of first n natural numbers.