求下列函数的 dfrac ({a)^2z}(a{x)^2} ,dfrac ({partial )^2z}(partial xpartial y) ,dfrac ({a)^2z}(a{y)^2} (其中f具有二阶连续偏导数):-|||-(1) z=f(xy,y) ;-|||-(2) =f(x,dfrac (x)(y)) ;-|||-(3) =f(x(y)^2,(x)^2y) ;-|||-(4) =f(sin x,cos y,(e)^x+y) .