Your idea matters-20(Reuploaded)

Algebra Level 3

1 3 + 2 3 + 3 3 + . . . . + n 3 = ( 1 + 2 + 3 + . . . . + n ) x 1^3+2^3+3^3+....+n^3=(1+2+3+....+n)^x , can it ever be?

The question is x + 4 = x+4= ?


The answer is 6.

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1 solution

Joshua Lowrance
Oct 19, 2019

For every single integer n n from 1 1 to \infty , 1 3 + 2 3 + 3 3 + + n 3 1^3+2^3+3^3+\cdots+n^3 will equal ( 1 + 2 + 3 + + n ) 2 (1+2+3+\cdots+n)^2 .

Proof:

Each of the squares has a different integer length, shown at the side of the graph. If you notice, we have one square with an area of 1 2 1^2 , two square with an area of 2 2 2^2 , three squares with an area of 3 3 3^3 , etc. In other words, 1 ( 1 2 ) + 2 ( 2 2 ) + 3 ( 3 2 ) + + n ( n 2 ) = 1 3 + 2 3 + 3 3 + + n 3 1(1^2)+2(2^2)+3(3^2)+\cdots+n(n^2)=1^3+2^3+3^3+\cdots+n^3 .

If you also notice, each time, the squares come to together to make a larger square (more or less). That square is actually equal to ( 1 + 2 + 3 + + n ) 2 (1+2+3+\cdots+n)^2 . However, in some of the cases, the squares overlap and leave a hole. However, the overlap and the hole are exactly equal, so we can say that ( 1 + 2 + 3 + + n ) 2 = 1 3 + 2 3 + 3 3 + + n 3 (1+2+3+\cdots+n)^2=1^3+2^3+3^3+\cdots+n^3 .

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