Find the sum of first n natural numbers.
n(n+1)2
The first n natural numbers are 1, 2, 3, 4,....., n.
This sequence forms an AP, whose first term is 1 and the common difference is 1.
The sum upto n terms of an AP is given by
Sn=n2[2a+(n−1)d].
Hence, the sum of the above AP is given by
Sn=n2[(2×1)+(n−1)1]
⇒Sn=n2[1+n]
=n(n+1)2