Hi : http://img841.imageshack.us/img841/9800/hviw.png

I was wondering, I undestand what the text in the given link says, but I don't understand why we don't consider square rooth of variables valid?

It says that a polynomials can only be constructed with addition, divison and substraction. The square rooth of two is a number, like any other, which can be used to construct a polynomial with these basic operation. Why can't we consider it in the same manner with square rooths of variables ????

Thank you.