A Particular Result

Algebra Level 2

Let S ( n ) = 1 + 2 + + n S(n)=1+2+\cdots+n be the sum of the first n n natural numbers and C ( n ) = 1 3 + 2 3 + + n 3 C(n)=1^3+2^3+\cdots+n^3 the sum of the first n n cubes. Then, what is the value of k k in C ( n ) = S k ( n ) C(n)=S^k(n) ?

None of the other answers k = 3 2 k=\displaystyle\frac{3}{2} k = 3 k=\sqrt{3} k = 3 k=3 k = 2 k=2

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1 solution

Tom Engelsman
Sep 8, 2018

For all n N n \in \mathbb{N} :

S ( n ) = n ( n + 1 ) 2 S(n) = \frac{n(n+1)}{2} and C ( n ) = n 2 ( n + 1 ) 2 4 C(n) = \frac{n^2 (n+1)^2}{4}

Hence, C ( n ) = S 2 ( n ) k = 2 . C(n) = S^{2}(n) \Rightarrow \boxed{k = 2}.

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