Understanding the 4-Ball: ||x|| ≤ r

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SUMMARY

The discussion focuses on understanding the mathematical concept of a 4-ball defined by the inequality ||x|| ≤ r, where the equation is expressed as x² + y² + z² + w² ≤ r². Participants clarify that the equation does not equate two expressions, emphasizing the need for an equals sign for a proper equation. The limits for the variables x, y, z, and w are explored, with specific ranges provided for each variable based on the constraints of the 4-ball. The conversation highlights the importance of precise mathematical terminology and understanding the geometric implications of the 4-ball.

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Homework Statement



What is the x-simple description of a 4-ball = { ||x|| [tex]\leq[/tex] r }

Homework Equations



It's a 4-ball, so isn't the equation x[tex]^{2}[/tex] + y^2 +z^2 +w^2 ?

The Attempt at a Solution


For my limits, I got x is between [tex]\pm[/tex] [tex]\sqrt{1-z^2}[/tex] and y is between -1 and 1, and z is between [tex]\pm[/tex] [tex]\sqrt{1-x^2-y^2}[/tex], and w is between [tex]\pm[/tex] [tex]\sqrt{1-x^2-y^2-z^2}[/tex] Is this right? Thanks!
 
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buuumppp...please help! Any advice is good!
 
stanford1463 said:

Homework Statement



What is the x-simple description of a 4-ball = { ||x|| [tex]\leq[/tex] r }

Homework Equations



It's a 4-ball, so isn't the equation x[tex]^{2}[/tex] + y^2 +z^2 +w^2 ?
That couldn't possibly be the equation. An equation always states that two expressions have the same value. I see only one expression, and even more to the point, I don't see an equals sign.

What does x-simple description mean?
stanford1463 said:

The Attempt at a Solution


For my limits, I got x is between [tex]\pm[/tex] [tex]\sqrt{1-z^2}[/tex] and y is between -1 and 1, and z is between [tex]\pm[/tex] [tex]\sqrt{1-x^2-y^2}[/tex], and w is between [tex]\pm[/tex] [tex]\sqrt{1-x^2-y^2-z^2}[/tex] Is this right? Thanks!

Where did the 1 come from?
 

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