partial_f(1,2)/partial_x=16
partial_f(1,4)/partial_x=64
partial_f(1,4)/partial_y=8
dz/dx=partial_f(x,f(x,y))/partial_x+partial_f(x,f(x,y))/partial_f(x,y)*parital_f(x,y)/partial_x
代入(1,2)坐标,有
f(x,f(x,y))=f(1,4)
dz/dx=partial_f(x,f(x,y))/partial_x+partial_f(x,f(x,y))/partial_f(x,y)*parital_f(x,y)/partial_x
=64+8*16
=192