# 4-ball B^4

1. Nov 11, 2008

### stanford1463

1. The problem statement, all variables and given/known data

What is the x-simple description of a 4-ball = { ||x|| $$\leq$$ r }

2. Relevant equations

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

3. The attempt at a solution
For my limits, I got x is between $$\pm$$ $$\sqrt{1-z^2}$$ and y is between -1 and 1, and z is between $$\pm$$ $$\sqrt{1-x^2-y^2}$$, and w is between $$\pm$$ $$\sqrt{1-x^2-y^2-z^2}$$ Is this right? Thanks!

2. Nov 11, 2008

### stanford1463

3. Nov 12, 2008

### Staff: Mentor

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?
Where did the 1 come from?