Function Field of Projective Variety

Question

In Silverman's Book, he defines function field of Projective Variety V, denoted as K(V), in that definition he says that for different choices of $\mathbb{A}^n$ (affine n-space), the different K(V) are canonically isomorphic. I am not getting any idea to prove this statement by using previously stated results in the same book or any different approach.