If (12−a1)+(22−a2)+(32−a3)+.......(n2−an)=13n(n2−1), then an is given by
A
n
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B
n2
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C
2n
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D
n2
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Solution
The correct option is An (12−a1)+(22−a2)+(32−a3)+.......(n2−an)=13n(n2−1) (12+22+32+....+n2)−(a1+a2+...+an)=13n(n2−1) n(n+1)(2n+1)6−13n(n2−1)=(a1+a2+...+an) ⇒a1+a2+...+an=n(n+1)2 ⇒an=n (Sum of first n natural numbers is n(n+1)2)