This is the Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE

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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.

Deepak BoraNewbie

# 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)