This is the Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE
Board.
In this Question you have to find the sum of first n natural numbers.
This is the Question Number 13 Of Exercise 11 D of RS Aggarwal Solution.
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Find the sum of first n natural numbers.
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Sn​=1+2+3+....+n
Sn​=2n​[2a+(n−1)d] where a=1,d=2−1=1
⇒Sn​=2n​[2×1+(n−1)1]
⇒Sn​=2n​(n+1)
∴ Sum of first n natural numbers=2n(n+1)​