What is the limit volume of this figure as n goes to infinity?

Calculus Level 3

Note: I am asking for a numeric answer. If you can determine the answer without actually figuring out the limit, then that is OK.

The absolute values of x x , y y and z z are 1 \leq 1 . n n is a positive even integer, i.e., n m o d 2 = 0 n \bmod 2=0 . The values are all R \mathbb{R} .

What is the limit as n + n\to +\infty from below of the volume of the figure such that ( x n + y n + z n ) 1 (x^n+y^n+z^n)\leq 1 is true and the absolute values of x x , y y and z z are 1 \leq 1 .

For your assistance, here are two pictures from the beginning of the sequence.

For n=2,

For n=4,

This is not a requirement to solve this problem. If you like, then determining this limit will give you a major clue:

Assuming [ x 1 , lim n lim x 1 x n ] \text{Assuming}\left[\left| x\right| \leq 1,\underset{n\to \infty }{\text{lim}}\ \underset{x\to 1}{\text{lim}} \ x^n\right]


The answer is 8.000.

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1 solution

The major clue limit is 1 1 . As the even integer n n goes to + +\infty from below, the figure becomes more cube-like. At the limit, it is a cube. The volume is 2 3 2^3 or 8 8 .

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