Find the sum of first n natural numbers.

Question:

Find the sum of first n natural numbers.

Solution:

The first n natural numbers are:

1, 2, 3, 4...

a = 1, = 1, Total terms = n

$S_{n}=\frac{n}{2}[2 a+(n-1) d]$

$\Rightarrow S_{n}=\frac{n}{2}[2 \times 1+(n-1) 1]$

$\Rightarrow S_{n}=\frac{n}{2}[2+(n-1) 1]$

$\Rightarrow S_{n}=\frac{n}{2}[n+1]$

 

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