# How many coordinates are necessary to determine a sphere?

Do determine a circle, you would need at least three coordinates. How many are necessary to determine a sphere?

-
Hint: why you need three points to determine a circle. In other words, given three points, how do you determine the circle? –  Patrick Li Nov 4 '12 at 17:16
I could take the bisections of two of the three points twice, and the intersection of those two lines would be the centre of the circle. The radius then is just the distance between the centre and one of the points. –  timvermeulen Nov 4 '12 at 17:20
So, to determine a sphere, I assume you would need three points again: taking the three bisections, see where those intersect and there's the centre of the circle. However, it doesn't seem logical to me a circle needs the same amount of coordinates to determine as a sphere. –  timvermeulen Nov 4 '12 at 17:24
In how many dimensions is your sphere embedded? –  Peter Taylor Nov 4 '12 at 17:26
@timjver Note that the bisection of two points in three dimension is a plane, not a line. –  Patrick Li Nov 4 '12 at 18:44