f(x)=ln((x-2)/(x-4))+x/4的导
＝1／((x-2)/(x-4))*｛〔(x-2)/(x-4)〕的导数｝+1/4
＝(x-4)／（x-2) ＊｛ 〔1+ 2/(x-4)〕导数｝+1/4
＝(x-4)／（x-2)* ｛ －4*2/(x-4）＾2｝+1/4
＝ -8／（x-4）*（x-2)+1/4