Answer:
The sum S of first n natural numbers is given by the formula S = n (n + 1 )2 .
Step-by-step explanation:
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Class 11>>Applied Mathematics>>Sequences and series>>Arithmetic progression>>The sum S of first n natura...
Question
The sum S of first n natural numbers is given by the formula S=2n(n+1).If S=231, find n
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Solution
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S=2n(n+1)
⇒231=2n(n+1)
⇒n2+n−462=0
⇒n2+22n−21n−462=0
⇒n(n+22)−21(n+22)=0
⇒(n+22)(n−21)=0
⇒n=−22 or n=21
∴n=21 as n=−22 is not a natural number.
