): 37 For a set of pairs of observations (x1, y), (x2,Yz), (**, Y.), prove that the total variation Ely: -3) can be written as Ely:-5)} = E(y; -y;';'+Ely;'-5) where yi' represents the values of y for given values of x = x3, x4, x, obtained from the regression equation of y on x. Explain the significance of the identity given above with reference to regression equations.[