If we take Q to be a subset of the R-vector space R, The convex hull is the minimal convex subset of R containing Q (going by the definition on wikipedia). Clearly R is convex and contains Q. Conversely, if C is the convex hull and x is a real number, then C contains rational numbers a,b such that a < x < b (since C contains Q), and so contains x since C is convex.
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Anonymous2009-04-19 14:53
is that like the hull of a ship, shouldn't a hull be concave or shit would fall out
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Anonymous2009-04-19 15:49
>>9
I guess that would depend on whether you were inside the ship, or outside; eh Pythagoras?