Question

# The formula of the sum of first n natural numbers is S=n(n+1)2. If the sum of first n natural number is 325, find n.

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Solution

## S=n(n+1)2=325n(n+1)=650n2+n−650=0−1±√(1)2+4(1)(650)2(1)−1±512−1±512 −1−512n=25n≠−25 as n is natural numbern+1=2625 and 26.

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