What is the meaning of "minimum dimensions to create a cylinder" ?
There are two dimensions : diameter=2r and height=h.
If you suppose that only one is minimum, the other will be maximum, which probably isn't what is expected.
So, it is logical to think that we are looking for both equal and minimum : h=2r The result is easy to obtain in this case.
A more complicated hypothesis might be to consider the largest distance between two points of the cylinder : L=sqrt(h²+(2r)²) and two find the dimensions so that L be minimum.
Since r=√(750/πh), we have L² = h²+4*750/nh from which a minimum valune for L can be derived.