Many of the applications of the x2 distribution can be justified as particular cases of a general theorem. It is the purpose of this paper to state and give a simple analytic proof of this theorem. Two of the more basic x2 principles are stated as corollaries of the general theorem. The usual procedure in developing the applications of x2 is to treat each application more or less independently. When proofs are included they usually involve geometry in n-space, the moment generating function, the Laplace transform, or the algebra of quadratic forms. The proof given here makes use of none of these methods. It does make use of the Jacobian in the change of variables in a multivariate differential (or multiple integral).