(weyl rescaling) only works because sheet is 2-dimensional
. To get it, find the extremal
path of a string. The integral to minimze is: 
where 
= 2 dimensional
metric on world sheet.
symmetries:
(weyl rescaling) only works because sheet is 2-dimensional
If you take the determinant, you'll get the argument of the integrla
of s. so 
. D=26 to avoid quantum mechanical problems.