# Calc III

1. Feb 2, 2009

### mamma_mia66

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

Write the equation of the sphere whose diameter has endpoints at (-1,1,-3) and (3,-1,2).

2. Relevant equations

3. The attempt at a solution

(x-x1)2+ (y-y1)2+ (z-z1)2= r2

the center of the sphere is : (1,0,-1/2)
r= $$\sqrt{}5/4$$

then the equation is: (x-1)2+(y-0)2+(z+1/2)2=5/4

Please someone check my answer and if I am not right, help me to solve it.

2. Feb 2, 2009

### tiny-tim

Hi mamma_mia66!

Centre is right.

But r is wrong.

(you've calculated the distance from the centre to the origin! )

3. Feb 2, 2009

### mamma_mia66

I am not sure that I know how to find the r ???? too old to remember it after so many years not being in school.

4. Feb 2, 2009

### tiny-tim

Yes you do!

they've given you a diameter

5. Feb 2, 2009

### mamma_mia66

r= sq. rt. (3-1)2+ (1-0)2+(2-1/2)2= 21/4

Last edited: Feb 2, 2009