Let Xn,20 f(X,) f(x (1)becomes V=6Zi0+b,Z1i+ +bi Zki+8i (2) where v=Y/5(X, ) ' =6/f(X,) The variance of the error term in(2) is constantLet (1) becomes (2) where The variance of the error term in (2) is constant. 0 1 1 , ( ) ( ) ji ji i i i Z X Z f f = = X X * V b Z b Z b Z i i i k ki i 0 0 1 1 = + + + +  * ( ) , ( ) V Y f f i i i i i i = = X X  